Surface Water: Lakes

A unique resource of the Borough of Mountain Lakes is the chain of man-made lakes within its borders. The bottoms of the lakes are fine sediments and organic material. Before construction of the dams, the lake areas consisted of swamps and woodland. The water source is from springs and surface drainage of land within the Borough. This geographical arrangement makes it possible for Mountain Lakes to provide more control of the surface water quality than is possible in most communities. Conversely, the responsibility for pollution falls squarely upon the residents. The total area of all of the nine lakes in the chain is approximately 162 acres.

The lakes provide recreation in all seasons. There are public swimming areas on two lakes, Birchwood and Mountain, and swimming from private docks and beaches is popular on all of the lakes. All of the sandy beaches in the Borough, both public and private, have been artificially created by bringing sand from other sources. Fishing is good with such species as bass, perch, pickerel, crappie, sunfish and catfish to be found in most of the lakes. Each spring a Trout Derby is held on Birchwood Lake for the children of the community. Those trout that are not caught, survive and continue to be caught throughout the summer. Trout will live in the lakes but will not breed, apparently because the summer water temperatures are too high. Sailboat races are held during the summer on Mountain Lake where some international class sailors have been developed. Canoeing is also very popular. During the winter there is skating on all lakes.

The lakes provide a haven and a home for many wild creatures. At one time muskrats became so numerous that a professional trapper was employed who took 124 muskrats from Birchwood and Crystal Lakes in just a few weeks. Since then they have again become well established. Several species of turtles are visible on logs and rocks around the shore during a warm summer day. In addition large snapping turtles can be seen occasionally in the upper lakes, especially in the spring when they leaves the water to lay eggs. There are also some non-poisonous water snakes in the upper lakes. Water fowl including Canada geese and several varieties of ducks stop on the lakes. Periodically a pair of swans nest on a few of the lakes.

The Lakes Management Committee has monitored and maintained the health of the lakes.  As part of their duties, the Committee has engaged the services of a lakes management consultant, Allied Biological, Inc. from Hackettstown NJ.  The Allied Program consists of weekly surveys of all lakes, biweekly unicellular phytoplankton sampling from June-August, herbicide and algaecide applications to control nuisance macrophytes and algae, and a water quality monitoring program (phytoplankton and water chemistry analysis).

The control of nuisance species and algae is necessary to preserve native flora and fauna populations and to maintain high lake water quality for all to enjoy.  Left uncontrolled, non-native invasives, like Eurasian watermilfoil, curly-leaf pondweed, water chestnut and purple loosestrife, develop into dense weed masses that literally suffocate the lake and fauna that depend upon it.  Similarly, excessive algae growth can develop into unsightly “blooms” with noxious odors and can dramatically lower the water clarity and oxygen needed for a healthy ecosystem.  Of particular concern, blue-green, or unicellular, algae are capable of producing toxins that cause skin irritation, allergic reactions, GI symptoms and respiratory problems.  This blue green algae and nuisance blooms have occurred in our lakes, namely Wildwood, Olive, Shadow and Grunden’s.  Algae thrives in nutrient-rich (phosphorus and nitrogen) waters caused by external sources like lawn fertilizers, stormwater runoff and wildlife droppings.  Even if external sources can be controlled, however, a significant amount of phosphorus can be released naturally from lake sediment found on the bottom of oxygen-challenged water bodies.

There are two ways to deal with lake management problems such as these:  “quick fix” and long-term management.  Under the direction of the Lakes Management Committee, Mountain Lakes is making efforts on both fronts.  As a short-term solution, The committee employ Allied Biological to apply herbicides, algaecides and use hydro raking to kill unwanted algae and invasives.  This process treats the biological symptoms of a lake’s problems but does not address the underlying causes.  Long-term management entails a coordinated effort of community groups, individuals, landowners and government.  Examples of long-term management efforts are Borough ordinances prohibiting the use of phosphorus-containing fertilizers and new efforts promoting the use of riparian buffers at the lakes’ edge.  The leading example of the latter is the Centennial Cove Project in which invasive bushes were removed and replaced with a 360 foot garden buffer containing native species.

A brief description of each lake follows detailing its historical name, individual characteristics and current remediation efforts.  This information was taken from the 2009 and 2010 Year End Lakes Management Reports prepared for the Borough by Allied Biological.  Of note, the water quality measures reported and subsequent treatment program are highly related to variables beyond our control like levels of precipitation and ambient temperature.  The summer of 2010 was one of the hottest and driest on record which dramatically increased water temperature and subsequent algae blooms.

Birchwood Lake (Third Lake)
Surrounded entirely by Borough-owned woodlands, this 14 acre lake has the best water quality because of its many springs. It also tends to be the coldest with surface water temperatures 1-2 C colder than the other lakes.  The lake is very shallow in the upper portion with an average depth of only 3 to 4 feet.  In the lower portion, where areas are designated for public swimming, the deepest areas are 12 to 15 feet. Recreationally, several platforms and floats are located for use in the extensive swimming and diving programs promoted here.

Birchwood is located at the beginning of the chain and gets little surface run-off because of the absorptive quality of the woodland soil. Hence, Birchwood features the highest plant diversity, the lowest alkalinity and pH (6.5), as well as the lowest phosphorus levels at .02 mg/L.  Phosphorus is a chemical compound derived from phosphorus and oxygen and is generally the limiting factor in aquatic plant growth. Phosphorus exists naturally in low levels, however, man-made phosphorus from fertilizers and septic systems enter freshwater during rain storms or as a result of bank erosion.  A total phosphorus level greater than .03 mg/L can promote excessive aquatic plant growth and decomposition in the form of algal blooms or nuisance plant growth.

Given all the positive lake quality measures listed above, a particularly perplexing problem has been a low level of dissolved oxygen.  Dissolved oxygen is the measurement of the amount of oxygen freely available to aquatic biota.  Factors affecting it include temperature (warm water holds less oxygen), atmospheric pressure (low pressure decreases solubility), mineral content of the water, water mixing (wind, flow or thermal upwelling) and an over abundance of organic matter such as dead algae.  Excessive dead materials cause rapid aerobic bacteria growth which, in turn, consumes a great deal of oxygen.  To support diverse aquatic biota, 5-6 mg/L of dissolved oxygen is minimally required.  At Birchwood early season water oxygen is at minimal levels of 5.09 (2010) and it declines by late June to as low as 1.66 mg/L.  Since 2007, this low oxygen level has prevented algae treatments with products like Alum.  Efforts to improve water oxygenation include the installation of an aerator in the swimming lanes and another opposite the beach.

Another area of concern has been siltation at the lower end caused by the construction of the public beach facilities and the replenishing of sand at the beach. An effort has been made to control sedimentation by constructing lakeside walls of wooden ties and of concrete.

Crystal Lake (Second Lake)
The second in the chain and the deepest, Crystal Lake is partially surrounded by Borough woodlands. As a result of its water purity, this lake and its adjacent lake were used for many years as sources of high quality ice for commercial and home use. It was during this era that these lakes were named First, Second and Third by the Fox Lakes Ice Company. Crystal has an area of 20 acres. The depth in the upper portion above the island is 4 to 8 feet. Between the island and the outflow dam the depth varies from 12 to 18 feet. Its depth, attractive natural surroundings and the variety of fish species has made this lake a favorite with fishermen in both summer and winter.

Although the lake once boasted pristine water quality, development in the 1970’s on both the east and west side of the lake, required more roads with storm drains leading to the lake. This development has resulted in an increase in sedimentation and a decline in water clarity, however, 2010 levels were quite good with an estimated 8 foot visibility in June.  Dissolved oxygen levels are excellent (6.8 mg/L to 8.6 mg/L) and phosphorus, while higher than historically (.02 mg/L to .03 mg/L), remains at acceptable levels.  Although problematic blue-green algae have been found in this lake as recently as 2008, the problem has not re-occurred.

Sunset Lake (First Lake)

The third lake in the chain, about one third of the total shoreline of Sunset Lake remains woodland along the northern and western shores. The area is 15 1/2 acres with an average depth of 6 to 8 feet.  Public access was provided in 1974 with an access road off of Pocono Rd. Dissolved oxygen levels at Sunset are good (6.5 mg/L to 7.0 mg/L), but turbidity is increasing and phosphorus levels were again high in late summer (.04 mg/L). Turbidity is the measurement of lack of water clarity caused by suspended solids.  The leading sources of turbidity include soil erosion, urban runoff, flooding, dredging and algae blooms.  Sunset’s 2010 turbidity ranged from 2.5 NTU to 4.6 – second only to Shadow (5-44 NTU) and Olive (6-7 NTU) lakes.  Sunset’s turbidity is showing a 3-year upward trend and if it continues to rise, it may negatively impact aquatic biota, especially fish.

Olive Pond and Shadow Lake
Next in the chain are the two connected lakes Shadow and Olive with a combined area of 3 1/2 acres. These ponds are surrounded almost entirely with private residential properties and roadways.  The average depths of these lakes are only 4 to 8 feet so the surface drainage from surrounding properties has resulted in excessive nutrients and sedimentation resulting in algae growths.  Recent dissolved oxygen measurements for Olive Lake have shown a range of 1.8 mg/L (dangerously low; 4.0 mg/L or lower can cause a fish kill if it persists) to 9.85 mg/L.   Although the latter looks ideal, due to the high water temperature, it was most likely caused by high phytoplankton counts resulting in a high level of photosynthesis. Total phosphorus levels ranging from .06 mg/L to .11 are, together with connecting Shadow Lake, the highest in the Borough.  Additionally, relatively high turbidity of 1.6 NTU to 6.0 NTU can be expected to have detrimental effects on aquatic biota.  Blue-green algae continues to be an issue with levels detected from July onwards; in recent years, algae treatments cannot be administered in late season because oxygen levels are too low to support it.

Similar to Olive Pond, Shadow Lake exhibits wide swings in dissolved oxygen levels (4.8 mg/L to 12.8) tied to excessive algae and water temperatures, and season-long elevated levels of phosphorus (.08 mg/L to .16).  In 2010 the new aeration system was operated continuously but given the extreme weather it was difficult to judge its effectiveness.  Of particular note, turbidity levels spiked to 44 NTU in July and although they declined to 5.2 in August, the cause of these extreme variables could not be determined. In response to the persistent high nutrient concentrations observed in this Lake, Allied Biological began fecal coliform sampling in the middle of the season and conducted sewer dye testing with 7 out of the 18 homes that border the lake.  The fecal data indicated very variable results and it was determined that a more comprehensive sampling study would be needed to determine the source of the observed bacteria although a residential source appears likely.  Lastly, the appearance of significant densities of blue-green algae, especially documented toxin-producers, is a cause for continued concern at Shadow Lake.

Mountain Lake
By far the largest lake with 79 acres, Mountain Lake has an average depth of about 6 to 8 feet in the area north of Island Beach and Midvale Dock. The balance of the lake has an average depth of 8 to 10 feet–slightly more near the dam. Normally the outlet at the dam is kept closed to force all available water to flow through Mountain Lake and on through the canal to Wildwood Lake.  When necessary, a system of valves control the system outflow for water level management, treatment of the lakes, and safety.

This lake provides the facility for sailboat racing and is a dramatic setting for the Fourth of July fireworks celebration. Island Beach, the public swimming area, is particularly attractive for smaller children because of the extensive area of shallow water and its pleasant beach. It is also very convenient because of its central location.

Dissolved oxygen levels at Mountain Lake are suitable although can be slightly low in early summer (4.9 mg/L to 7.4 mg.L).  Phosphorus levels are higher than desirable (ranging from .05 mg/L to .07 mg/L), resulting in moderate to high algae densities in late season. There are also certain areas where sedimentation has caused some filling of shore-line areas.

Cove (Propagation Pool)
The Cove has a surface area of one acre and given its central location on Morris Avenue, is a popular place for ice-skating in the winter.  In 2011 it was the site of a comprehensive landscape/hardscape re-design in honor of the Borough’s 100 year anniversary.  Run by volunteers, the “Centennial Legacy Project” removed existing invasive species and created a riparian buffer of natural plant species between the street and the lake.  The Project recently won the 2011 ANJEC Environmental Achievement Award and the volunteers had an opportunity to share their work with Environmental Commissions throughout the state.

In terms of water quality, the Cove’s low dissolved oxygen levels ranging from 3 mg/L to 5 mg/L are a continual cause for concern. The addition of an aerator may improve ecological conditions.  Phosphorus levels are elevated at .04 mg/L to .06 which is not surprising considering the high phosphorus measurements upstream at Olive and Shadow Lake.

Grunden’s Pond (Reservoir Lake)
Located across the Boulevard, Grunden’s Pond measures 2 1/2 acres.  Dissolved oxygen levels (5.9 mg/L to 9.3) are considered adequate and although an aerator was thought to be necessary in this location, recent data indicates that it may not be needed.  Phosphorus levels varied throughout the season but were overall too high, ranging from .03 mg/L to a high of .06 mg/L.  Field biologists also noted turbid conditions despite low rainfall and decreased observations of carp and koi.  Additional testing parameters were added to Allied’s Program in 2009 with tests undertaken to understand ammonia, carbon dioxide, iron and calcium levels.  It has been determined that ammonia levels are undetectable indicating that the nitrogen cycle is in balance.  Carbon dioxide has been found at elevated levels which could be suppressing dissolved oxygen.  Iron is a micro-nutrient released into water bodies naturally via rock weathering or from human sources such as acid rain.  When it is present at high levels, it can contribute to blue-green algae formation.  At Grunden’s Pond, iron levels increased throughout the 2010 season from .26 mg/L to a high of .91 mg/L in August (Secondary Drinking Water Regulations limit iron at .3 mg/L).  This build up could be a result of low rain conditions that failed to flush the iron out of the Pond and did not seem to contribute to excessive algae.



Wildwood Lake
This is the final lake in the chain. It is slightly over 26 acres in area and has an average depth of 3 to 4 feet in the end nearest the Boulevard and of 6 to 8 feet for the balance of the lake.  It is slightly deeper near the dam. There are two small streams which flow into the lake on the north end near the Boulevard. They come from springs located up the hill in the vicinity of Laurel Hill Road. The lake is surrounded mostly by private property with some small Borough-owned sections. Dissolved oxygen levels are good at 5.2 mg/L to 7.9, however, phosphorus levels are high measuring .17 mg/L in July of 2010.  Algae blooms have been a re-occurring problem at this lake although the need for algaecides has been decreasing since 2008.



Dixon’s Pond
This is a privately-owned pond of less than an acre at Valley Road.

Arrowhead Lake, Great Bay and the Bay of Deep Waters
In 1925 the Arthur D. Crane Co. purchased 100 acres, including a small lake called Protectory Pond, from the Sisters of the Sorrowful Mother of St. Francis Health Resort. Combining this land purchase with two smaller ones, the Crane Co. began development of a lake community which would lie within the borders of both Mountain Lakes and Denville.

In the fall of 1925 a dam was constructed and Protectory Pond was flooded using its own natural springs. This newly formed body of water was called Arrowhead Lake. Aided by their natural springs, two small swamps were later transformed into two additional lakes named the Bay of Deep Waters and Great Bay. These three bodies of water cover approximately 34 acres and lie, on average, 525 feet above sea level.

Arthur Crane’s plan was to build a summer community of privately owned houses. Many of these second homes were owned by people who spent most of the year living in Brooklyn and Jersey City. After the stock market crash of 1929, some of these people found it impossible to continue maintaining two residences. Soon the beautiful lakes and pleasant surroundings encouraged more and more people to make Lake Arrowhead their year round home.