Lake Isis
Lake Isis is a fairly deep, sandy-bottomed 'ridge' type lake located just north of the City of Avon Park. Water quality in Lake Isis is fair, based on Lakewatch data, with the potential of being poor due to extremely high nitrogen levels. Phosphorus levels in Lake Isis are quite low, ranging from 2 to 14 ppb (parts per billion) and averaging 5 ppb. However, nitrogen levels are among the highest of any lake in the county, ranging from 1580 to 5290 ppb, and averaging 2833 ppb, well above the expected range for a lake of this type and well above the expected range of even the nutrient enriched transition type lakes. This excess nitrogen is probably derived from external sources, possibly including inorganic fertilizer use on home lawns and in agriculture. Algae levels, as measured by the concentration of chlorophyll in the water, are very low as a result of low phosphorus levels. Chlorophyll ranges from 1 to 6 ppb and averages only 2 ppb, though this level has the potential to increase dramatically if phosphorus is added to the lake. The addition of phosphorus might cause noxious algae blooms in the presence of very high nitrogen levels. Water clarity, as measured by the depth to which a standardized 'secchi' disc can be seen when lowered into the water, is quite good as a result of low algae levels. Secchi depths range from 12 to 30 feet and average 20 feet, making Lake Isis among the clearest lakes in the county. Water clarity will dramatically decline if algal levels increase. Water quality in Lake Isis is very similar to water quality in Lake Byrd, based on the limited data available. No long term trends can be determined with the limited data available. Sources of nitrogen in the Lake Isis watershed should be determined and addressed to prevent further water quality degradation. Click here to view water quality data by year.