When it disappears from view, the length of rope in the water is recorded. This information establishes how deep sunlight will penetrate into the water column . Most other lake organisms rely on plant growth for their own sustenance. Nutrient levels ultimately control the growth of all lake organisms. Dissolved concentrations of ammonia, nitrate, orthophosphate and total phosphorus are periodically monitored in many lakes.
Acceptable levels vary with each nutrient and for each lake situation.
Generally lower levels are preferred, with higher levels suggesting management problems like fertilizer runoff or surface outbreaks from septic systems. Bacteriological contamination can be routinely checked at an inexpensive cost through hospital, county health departments and consultant laboratories. New York State certifies some, but not all, of these laboratories. If coliform bacteria, common intestinal microbes, are found in the lake water then a recent episode of fecal contamination is indicated. Faulty septic systems, barnyard runoff or large numbers of migratory waterfowl are usually suspect.