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State of New Jersey-Department of Environmental Protection-Division of Water Monitoring and Standards
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Bureau of Freshwater & Biological Monitoring

Lake Monitoring Lakes Fact Sheet


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For every sampling event within a lake, on-site measurements of physical and chemical parameters are taken throughout the water column. Many parameters such as pH and dissolved oxygen need to be measured on site since they are affected by water temperature and other factors.

BFBM is certified by the Office of Quality Assurance (certified lab ID # 11896) for the following parameters during field work for this project: temperature, pH, conductance, dissolved oxygen (DO), turbidity, chlorophyll, and microcystins.

Daily calibrations of meters help ensure both precision and accuracy of these field readings. Standards of known concentrations are used to calibrate and perform checks on meters before each sampling event.

Click below to learn more about the parameters measured by BFBM staff.

Measures dissolved oxygen concentration and percent saturation as well as barometric pressure and water temperature. Since dissolved oxygen is inversely related to temperature, it is important to measure water temperature and barometric pressure concurrently. Adequate dissolved oxygen is essential for a healthy aquatic biological community. Low dissolved oxygen levels may be an indicator of excessive biological activity related to the decomposition of organic material, but also may be a natural condition related to certain types of waterbodies.

Measured on a scale of 0 to 14, this probe measures the pH of a lake, whether it is acidic (values less than 7) or basic/alkaline (values greater than 7). The acidity of New Jersey lakes can vary greatly depending on the underlying geology. For example, lakes in and near the Pine Barrens are naturally acidic (typically with pH of 3.5 to 5.5); a byproduct of the sandy acidic soil in the region, while most lakes in northern New Jersey are more alkaline (pH of 6.5 – 8.5) due to the local geology and soils found there. The pH value affects aquatic life directly (certain fish and other aquatic life cannot survive in waterbodies with pH values which are too low or too high) and the availability of certain chemicals and nutrients.

Measures specific conductance, which is the ability of water to conduct electrical current. Specific conductance is based on the relative number of ions dissolved in water. High conductivity can indicate high concentrations of ions, some of which are detrimental to aquatic life.

Measured on a scale of 0 – 400 µg/L. This probe measures the amount of chlorophyll a (green pigment found in plants) and the amount of Phycocyanin (blue pigment found in cyanobacteria). There is an increasing presence of HABs (Harmful Algal Blooms) in New Jersey’s waters. HABs can be dangerous to humans and animals. More information on HABs and the Department’s HAB strategy can be found at: Division HAB page.

Measures the clarity of the water, which is related to the ability of light to penetrate. The more light scattered by sediments and other materials in the water, the higher the turbidity. Higher turbidity results in a decreased opportunity for photosynthesis and lower dissolved oxygen levels. High turbidity in a lake can indicate issues with runoff and erosion, which results in increased sedimentation. Too much sedimentation can destroy habitat for aquatic life by burying important spawning areas or smothering biological communities.

To properly characterize the chemical and physical parameters of a lake, multiple stations that account for the morphometry of the lake and incoming streams are established. Once a station is established, water chemistry and physical parameters of the water column are measured. Depending on the total depth, water is collected via horizontal sampler for laboratory analysis. Two types of samples are collected:

(1) total (non-filtered) samples that contain suspended materials from the water column. Certain constituents can adhere to or be transported by suspended sediment and/or particulates.

(2) dissolved (filtered) samples are samples that have had particulates removed. Dissolved components tend to be more biologically available and mobile and thus are more susceptible to uptake by fish and other aquatic organisms.

Bathymetric surveying produces a detailed map of a waterbody’s depth and subsurface contours. This data can be used to calculate waterbody volume and coupled with other data to find the residence time of lake waters. These data aid in the development of water quality standards and Total Maximum Daily Loads (TMDLs). It can also aid in the management of aquatic vegetation, Harmful Algal Blooms (HABs), fisheries and water safety plans.

BFBM personnel use sonar equipped fish finders to log depths linked to GPS data. Lakes are traversed using predetermined transects to ensure accurate coverage of the entire lake. The data logs are then uploaded to a cloud-based software for processing. The resulting data is translated into detailed bathymetric maps of waterbodies throughout the State.

BFBM personnel have cored the sediment of many lakes throughout the State. Core samples can be used for a variety of purposes. These include diatom assemblage identification, nutrient/eutrophication status and analysis for pollutants. A maps of these lakes can be viewed using the Lake Mapper button below. Many of these sediment samples have been prepped by the Academy of Natural Sciences of Drexel University. A list of these lakes is available for download or viewing here.

Photo Credit: NJDEP

Photo Credit: NJDEP

Photo Credit: NJDEP

The physical habitat (PHab) characterization method was utilized by the USEPA as part of the National Lakes Assessment (NLA). BFBM employed this method beginning in 2013 as supplemental data to support assessments of lake water quality. The PHab survey estimates, measures and observes various conditions in the littoral and riparian habitat along lake shorelines. PHab surveys were performed through 2021 and will continue as needed and resources allow.

More information can be found on the U.S. EPA website (

Harmful algal blooms have become increasingly prevalent in freshwater waterbodies throughout the State. Under certain conditions, a cyanobacteria population can rapidly increase in density, forming a bloom which can potentially produce toxins, called cyanotoxins. These cyanobacteria blooms are known as harmful algal blooms (HABs). HABs can be found on the surface or throughout the water column. BFBM can detect and collect surface and subsurface HABs. Using a phycocyanin probe and a horizontal sampler, BFBM can measure the entire water column for the presence or absence of PC. For more information please visit the Department's HAB page.

Photo Credit: NJDEP

Photo Credit: NJDEP

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For more information, please contact Johannus Franken, Project Manager,
Bureau of Freshwater and Biological Monitoring at (609) 292-0427.

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Last Updated: August 17, 2022