This year, LLA is fully implementing the precipitation-based E. coli prediction model to estimate “real-time” estimates of E. coli levels in Lake Linganore.  The model was developed by Hood College under Friends of the Lake committee based on USEPA’s Virtual Beach Model. This model was calibrated to the Lake Linganore watershed using actual precipitation and E. coli data from the most recent 5 years (2019-2024). 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. Depending on model accuracy this season, the model may be used in the future to replace some or all of the sampling / lab analyses which are always 1-day old and inherently expensive. 

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 regularly 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.

Over 5 consecutive years of monitoring (2013 – 2017) the geometric mean E. coli concentration of Lake Linganore during the summer season ranged from 26 MPN / 100 milliliters (2017) to 39 MPN / 100 milliliters (2013), a range that is well below Maryland’s mean standard of 126 MPN / 100 milliliters. During these same five years, the number of days that E. Coli exceeded Maryland’s BAV ranged from 7 days (2014) to 22 days (2013) with an average of 13 days / season.

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 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 field readings.   Cyanobacteria become a greater concern when PC readings rise rapidly and are well in excess of 100 ug/L.    When PC and or criteria are exceeded, toxin test strips are used to determine if Maryland Department of the Environment (MDE) may conduct additional testing.