For everyone who depends on Keuka Lake, limnology - the study of the lake - is an important tool for protecting this irreplaceable resource. By studying the characteristics of Keuka Lake, managers can determine its condition and suitability for different uses, all of which (pure drinking water, good fishing, pleasant swimming conditions) depend on the quality of the lake's water.
That in turn depends on the activities that occur in the watershed. The impact of land use practices can be detected by monitoring and testing tributary streams, groundwater, and the lake itself. Over the past several decades, numerous water quality studies have been conducted on Keuka Lake and tributary waters. This program allows managers to: 1) detect trends in the health of the lake system; 2) identify new threats to Keuka Lake in a timely fashion; 3) determine sources and impacts of pollutants; and 4) evaluate watershed management programs.
Algae or phytoplankton are microscopic green plants that form the base of the lake food chain. They are the "primary producers" of food, converting sunlight energy to green plant material for all the "consumer" organisms in the lake. There is a dynamic balance between having just enough algae to support a healthy fish population and having too much algae, so the lake looks like "pea soup." Since chlorophyll is the primary plant pigment found in algae, measuring the concentration of the pigment in the lake provides a good indication of algae abundance. Pigment concentrations can also be used to estimate the overall lake aging condition or trophic status of the lake.
The mean chlorophyll concentration between 1991 and 1998 for Keuka Lake was 4.31 ppb. These levels mean the lake is moderately productive with respect to algae. Interestingly, the lake has significantly more than expected algae, given the low phosphorus levels in the lake. That means more food (i.e., plant material) is available at the bottom of the food chain, resulting in a larger forage base of small fish for the lake trout population.
Fecal Coliform Testing: The presence of fecal coliform bacteria in the lake indicate the presence of human or animal excrement. While fecal coliform bacteria are not harmful, they indicate that disease-causing bacteria or viruses may also be present. Swimming or drinking water from a lake contaminated with human sewage can cause serious health disorders such as dysentery, giardiasis, typhoid and other gastrointestinal infections. Fecal coliform testing is very important, since the lake provides water for nearly 3,000 homes, many of which use the water directly for drinking.
In general, the majority of the lake sampling sites show low fecal coliform counts, often less than 20 counts per sample (100 milliliters). Average levels are very low in June, rise in July and August, and then drop again in September. The worst levels have been recorded in July, particularly after a heavy use weekend, such as the Fourth of July. Fortunately, bacteria levels seem to be dropping, perhaps due to the extensive septic system work conducted by the wastewater program.
While many people drink untreated water from Keuka, it is not recommended, regardless of testing results. All surface waters are considered "open systems" and are vulnerable to runoff contamination from a variety of sources. Therefore, lakeshore residents are advised to disinfect lake water by chlorination, ultra-violet or some other Health Department recommended method. For more information on this subject, see the Keuka Lake Book, distributed by the KLA or Cornell Cooperative Extension, Yates County.
Zebra Mussels: Zebra mussel larvae were first discovered in 1994 in the East Branch near Penn Yan. Since then, the zebra mussel population has spread around the entire lake, although as of 1998, it had not reached the mat growth stage. The growth of zebra mussels in Keuka appears to be much slower than in other Finger Lake waters. One possible explanation is that zebra mussel larvae are being controlled by the lake's large alewife and smelt population. At this time, it is difficult to predict how the zebra mussel population will affect fisheries and human uses on Keuka Lake.
Fisheries: Keuka Lake is considered one of the best naturally spawning trout fisheries in New York State. Cold Brook remains the best nursery stream for rainbow trout. The rainbow fishery is considered all "wild" and is doing fairly well. Sugar Creek has a very good potential as a nursery habitat. Unfortunately, too many obstructions (beaver dams, logs, etc.) block the passage of spawning fish. Significant habitat improvement is needed to restore Sugar Creek to its potential. The warm water fishery is also doing well and is dominated by yellow perch and smallmouth bass.
Fish Tissue Contamination: DDT, widely used as a pesticide in the 1940's through the 1960's, is extremely persistent and fat soluble, leading to many environmental problems. Studies showed that it accumulated in the food chain, causing problems with bird reproduction and threatening human health. The Federal government ultimately banned DDT and its use was discontinued around 1970.
During the following decades, NYS DEC studies of lake trout from Keuka showed increasing levels of DDT. As a result, the NYS Department of Health issued a "fish consumption advisory" suggesting that no more than one fish per month over 25 inches be consumed. Pregnant women and children were advised to avoid eating trout altogether. Fortunately, DDT levels have declined dramatically since 1991 and may result in lifting the health advisory altogether if the trend continues.
Where the DDT came from in the first place is still unknown. One possibility is widespread, low-level amounts washing into the lake from fields where DDT was used. The current decline, therefore, may reflect improvements farmers have made in soil and water conservation over the last 25 years. Another possibility: discrete source(s), such as old dumpsites, where corroded containers may have leached DDT over an extended period of time. Both scenarios are likely.
Lake Chemistry and Physical Factors
Dissolved oxygen (DO) and temperature are important controls of biological activity in the lake. High water temperatures result in lower DO levels, while colder water is able to hold larger amounts of oxygen. Since oxygen is used by fish and other aquatic organisms for respiration, low DO levels can result in low fish production rates. In severe cases, it can cause suffocation or a fish kill. Oxygen depletion can occur when bacteria decompose excessive amounts of organic materials (dead algae, yard wastes, etc.) Oxygen depletion can also occur during the winter as organisms use up the available oxygen in lakes covered by ice for prolonged periods. To date, oxygen depletion problems have not been reported and studies indicate that the lake is well oxygenated to support a productive fishery.
Phosphorus and nitrogen are the most important nutrients supporting the food chain in the lake. These nutrients are the essential building blocks of life for aquatic plants, microscopic animals, and fish. Generally, phosphorus is the most critical nutrient since it usually is in limited supply. Excessive loading of phosphorus from sources like failed septic systems can result in algae blooms and lake eutrophication or aging. Algae blooms can create unsightly and foul smelling surface films. In severe instances, they can deplete the lake's oxygen supply to the point where fish mortality may occur. From 1992 to 1998, Keuka's total phosphorous levels ranged from 7.4 to 14.0 parts per billion (ppb). At these levels, the lake is not in danger of premature lake aging or eutrophication.
Normally, nitrogen is not a serious problem in surface waters. Nitrate can be a major health problem in drinking water when the concentration approaches 10 ppm. Keuka Lake nitrate levels remain well under 1 ppm (0.14 ppm average), indicating that there is no problem with nitrate contamination.
Water clarity provides a good indication of water quality by indirectly measuring the amount of suspended solids, algae, and zooplankton. Water clarity is measured with a Secchi disk - a simple tool consisting of a measured line attached to a disk which is lowered into the water until it disappears from view. The average secchi disk measurement for the lake is approximately 5 meters, with seasonal variations ranging from 2 to 9 meters. Water clarity seems to be gradually increasing, a trend that may rise with the spread of zebra mussels in the lake. Zebra mussels filter large volumes of water, greatly reducing the amount of algae and zooplankton, and increasing water clarity.
Keuka Lake is rimmed with 12 major tributaries and hundreds of smaller streams that only flow during snowmelt and heavy rain. Together these streams contribute large amounts of sediments and nutrients to the lake. Sediment plumes can often be seen after periods of heavy rain or snowmelt. These events can send water into the lake with nutrient levels from two to thirty times normal, indicating the impact a single event can have on the lake's overall nutrient level.
Summary and Conclusions
The testing results for Keuka Lake indicate the lake, overall, is in very good condition. The waters are relatively clear, contain low nutrient levels and have a sufficient algae growth to support excellent fisheries. The exceptions are bacterial levels and runoff following storm events. Bacterial levels continue as a concern, particularly in July. However, recent results may signal a decline, perhaps due to the new septic inspection program. Depending on the severity of a storm, the lake may take days or even months to recover from severe storms. Since nutrients and toxics are usually attached to sediment particles, controlling runoff from watershed lands is the key to preventing nutrients and toxics from entering the lake. A future unknown is the impact of zebra mussels. Certainly the lake will become clearer, but will there be more aquatic weeds and will the lake trout fishery suffer? Time will tell.