The Lakes
Lake Linganore is the largest of the four community lakes. Two beaches can be found along the lake in the villages of Nightingale and Coldstream. Lake Merle in Meadows Village is the second largest and has a small beach area on its eastern end. The remaining two lakes are Lake Anita Louise in Pinehurst Village and Lake Marion in Woodridge Village (the smallest of the four).

Lake Linganore water is used as the primary source of drinking water for the City of Frederick and is the emergency back-up water supply for Frederick County. It currently holds over 500-million gallons of water, nearly a four-month drinking water supply for the City of Frederick. The lake water comes from a ~80-square mile watershed roughly bounded by Mount Airy to the southeast, Taylorsville to the northeast, Libertytown to the northwest and New Market to the southwest. Water enters the lake through the two primary tributaries, Linganore Creek and Ben’s Branch, and leaves via the dam’s spillway at an average rate of more than 600 gallons per second, a flow that would fill an Olympic swimming pool in less than 20 minutes. While the Lake Linganore private community holds title to the land beneath and around the water, the water itself is public property. Members of the Lake Linganore community have been enjoying the waters of Lake Linganore for swimming, boating, fishing and other recreational purposes for decades.


Since Linganore Creek was dammed to create the lake in 1972, agricultural management practices in the Lake Linganore watershed have improved to help reduce harmful chemical applications to crops / fields and minimize livestock encroachment in tributaries and control run-off. Despite these better agriculture management practices, population growth has added new stresses to the environment and there continues to be room for further improvement of Lake Linganore water quality much like many freshwater lakes.


The lake is located in a county that is a leader in agricultural land use and milk production and in a state where agriculture is the largest commercial industry and the largest single land use. Lake Linganore likely is no exception to the United State Environmental Protection Agency’s (USEPA’s) 2000 findings from a study of the nation’s lakes that agriculture is the most wide-spread source of damage to lake quality. Algae nutrients and sedimentation were listed in the USEPA study as the top identified pollutants and stressors to U.S. freshwater lakes. Because of the agricultural land use of the Lake Linganore watershed and lake water quality observations, LLA Committee, Friends of the Lake, and its' Water Quality (WQ) subcommittee, has been focused on three main water quality aspects: algae nutrients; sedimentation; and bacteria. 

Lake Linganore Water Testing

LLA posts water test results Monday through Friday (excluding holidays) from Memorial Day to Labor Day. LLA Committee, Friends of the Lake, typically posts daily on Facebook (Friends of the Lake • Lake Linganore at Eaglehead).

Friends of the Lake operates a precipitation-based E. coli prediction model to provide “real time” estimates of E. coli levels in Lake Linganore. The model was developed USEPA and calibrated to many years of Lake Linganore data by Hood College. The USEPA’s Virtual Beach model is recalibrated each year to the Lake Linganore watershed using actual precipitation and E. coli data from 2016 onward. The prediction is based primarily on watershed precipitation totals for each of the prior three days but is also accounts for seasonal influences. Daily watershed precipitation data are derived from local weather stations, including one station maintained in our own community by a resident. The model may eventually replace some or all of the sampling / lab analyses which are always 1-day old and inherently expensive. 

Lake Linganore Water Test Results

As always, you can review water test results Monday through Friday (excluding holidays) from Memorial Day to Labor Day at or by scanning the QR code at the beaches. LLA Committee, Friends of the Lake,
typically posts daily on Facebook (Friends of the Lake • Lake Linganore at Eaglehead).

Lake Linganore water testing is conducted from Memorial Day to Labor Day. Water test samples are collected in the mornings from Nightingale Beach (from Lake Linganore), and the results are posted the following day (i.e., the results from samples taken the evening of August 28 are posted on August 29).

Daily model predictions are posted (Memorial Day – Labor Day) on the probability (low, moderate or high) that beach E. Coli concentrations will exceed the Maryland Public Beach Action Value (BAV).

Please note that there will likely be some contradictions between the E. coli model predication and inferences made from the prior day’s E-coli testing results. Residents will need to use their own decisions on lake use based on the best available information provided.

Understanding the Results

  • E.coli: 235 MPN/100ml is EPA’s / MDE’s Public Beach Action Value (BAV). Recreators in waters with E. coli exceeding the BAV, risk illness (at a rate exceeding 1 in 28 people).
      • E. coli concentrations can “spike” after it rains. So, as long as it doesn’t rain, you can use the prior day E. coli concentration to make decisions about today. Lake Linganore is no exception to Maryland Department of the Environment’s general advice that “…you should avoid swimming in natural waters within 48 hours of a heavy rain event…”.
  • PC (phycocyanin): >50 ug/L indicates the potential for an elevated cyanobacteria (blue-green algae) population.  Depending on associated CHL concentration and PC/CHL ratio trends, additional sampling and laboratory testing may be warranted to determine whether toxin-producing cyanobacteria and toxins are present.
  • CHL (chlorophyl): >100 ug/L indicates the potential abundance of total phytoplankton, including green algae and cyanobacteria.  This could present aesthetic issues or depending on the PC/CHL ratio trends could signal a potential algae bloom warranting further testing
  • PC/CHL: This ratio estimates the relative proportion of phytoplankton mass that is cyanobacteria.  If this ratio trends sharply and consistently higher over multiple days, it could signal the formation of a cyanobacteria bloom.   

Water Testing Frequently Asked Questions

E. coli is an accepted indicator of the possible presence of bacteria or viruses in water which could cause illness. The test used for E. coli is far less expensive and more reliable than other tests. Data can be used to correlate to precipitation data, identify / remedy sources and keep the Linganore community better apprised of water quality.

E. coli or Escherichia coli is a type of bacteria commonly found in the intestines and wastes of healthy warm-blooded animals (humans included). There are more than 100 different strains of E. coli, and most are harmless. E. coli O157:H7 is one strain of E. coli (usually associated with cattle, but has found in the intestines of deer, goats and sheep) that can cause illness.

Laboratories normally present testing results in units of most probable number (MPN) of bacteria colony-forming units (CFU) per 100 milliliters.

The primary source of E. coli in Lake Linganore is believed to be agricultural storm water runoff (e.g., manure) from farms in the 88 square miles draining into Lake Linganore. Higher levels can be expected during or after rainfall events. Suspended sediments and algae are believed to prolong the survivability of E. coli in lake water.

The lake water is sampled daily at Nightingale Beach during the summer season (Memorial Day through Labor Day). Results are available to the community within 1 day of sampling (the laboratory must culture the sample on an agar plate overnight for the analysis). Because the reported results are not “real-time” and conditions vary / change rapidly throughout the lake, residents should be aware that the results may not be representative of the actual water quality.   

Maryland’s public beach standards are an unenforceable point of reference for Linganore’s private beaches.  For public beaches, USEPA / Maryland has established a beach action value (BAV) of 235 MPN/ 100 milliliters.

In 2023, the beach E. coli concentrations exceeded the Maryland BAV on 3 days from Memorial Day through Labor Day.  During the same interval in other years the BAV was exceeded on 1 day (2022), on 10 days (2021), on 12 days (2020),  on 13 days (2019),  on 43 days (2018), on 9 days (2017), on 10 days (2016), on 19 days (2015) and on 7 days (2014).

Lake Linganore has been used for recreation for 50 years. During this time no known serious illness or injury due to E. coli exposure has been documented. Over the years, significant improvements have been made to County agricultural land and waste management practices to increase surface water quality. Residents have used and continue to use the private lake at their own risk. As with any lake, residents can reduce risks of contracting waterborne illnesses by not swallowing lake water and minimizing contact after rainfall events, during periods of excessive algae or siltation or when E. coli levels are higher than normal.  Lake Linganore is no exception to Maryland Department of the Environment’s general advice that “…you should avoid swimming in natural waters within 48 hours of a heavy rain event…”.

Phycocyanin (PC) is a pigment-protein complex found in cyanobacteria (also called blue-green algae). Because it fluoresces at certain wavelengths, PC can be conveniently and cost effectively semi-quantitatively measured in real time with field light reflectance instrumentation (especially if sampling personnel are already present sampling for E. coli). PC is a surrogate / indictor for the possible presence of cyanobacteria. Cyanobacteria are of interest because they can produce natural toxins that may be irritating or hazardous to recreational users and pets.  Cyanobacteria are routinely present in the community lakes including Lake Linganore.  Concentrations of cyanobacteria typically increase through the warmer months and late into fall.   Because field testing for PC is semi-quantitative screening method, further quantitative testing for cyanobacteria / toxins occurs if warranted by elevated or rapidly rising PC/CHL ratio field readings.   Cyanobacteria become a greater concern when PC/CHL readings rise rapidly and PC is >50ug/L.    When PC & CHL are elevated and the PC/CHL ratio increases over days, this may signal a potential cyanobacteria bloom.  If this occurs colorimetric test strips can be used to determine the potential presence of cyanobacteria toxins and Maryland Department of the Environment (MDE) can be asked to conduct additional testing.