by
Bob Werner
Skaneateles Lake Association
Over the last two weeks we have suffered some seriously heavy rainfall in the Skaneateles Lake watershed. The City of Syracuse gauges at the south end of the lake recorded 5.2 inches from June 30 to July 2 and 3.54 inches from July 13 to 15. During these rainy periods the rain fell heavily during a very short period of time, reaching nearly an inch of rainfall over approximately 20 minutes in one case. With the soil already saturated water poured down every stream and creek with great force eroding the stream banks and carrying silt, nutrients and debris into the lake. In addition, to that many cliffs along the shoreline broke loose and fell into the lake carrying more soil and rock with it.
What impact is this likely to have on Skaneateles Lake?
One obvious effect is the reduction in water clarity. Just days before the first storm the Skaneateles Lake Association measured water clarity in the middle of the lake using a Secchi disc. They were able to visually follow the disc down to about 30 feet before it disappeared from sight. This measurement was repeated 2 days after the first storm (July 1-2) and the reading had dropped to under 10 feet.  Two days later it had worked its way up to 13 feet. One thing that Skaneateles Lake is known for is the clarity of its water. It is not looking very clear now.
Once the silt settles out of the water, which it will do over the next few weeks, it provides a prime habitat for milfoil growth. Deltas are formed or enlarged at the mouths of streams. The accumulating silt is a perfect environment for fragments of milfoil that have broken off to settle, put out roots and grow into an established milfoil plant.
The third major effect is the addition of significant amounts of nutrients, particularly phosphorus and nitrogen washed in from the water shed. This will certainly stimulate plant growth in the lake, particularly algae. We can expect to see more algae than we have seen over the previous few summers.
Along with the nutrients washing in off of the watershed it is likely that dissolved organic material such as tannins and humic acids will be carried into the lake. Dissolved organic matter can act as a surfactant thus facilitating the formation of foam when the surface is agitated by wind or other factors.
One complicating factor that argues for a large impact is the timing of the rainfall. It has occurred relatively early in the growing season providing ample opportunity for algae and rooted aquatic plants to take advantage and increase their seasonal growth.
Given all of this it is clear that heavy rainfall and the accompanying erosion is not good for the lake.  We are likely to see increased algal growth, more patches of milfoil developing this summer and more foam forming over the course of the summer.
Source : Skaneateles PressÂ