Highland Lakes

Late last week a fish kill of more than 400 panfish (bluegills and perch) was found to have occurred in Lake 5 (Beach 7) from unknown causes. On May 23 a few hundred dead fish were found in the Main Lake and another 40 were discovered on Lake 4 (Beach 5). Dr. Stephen Souza, Ph.D. of Princeton Hydro, was called in for consultation with each occurrence and he is working closely with Allied Biological and the NJDEP Bureau of Fish and Wildlife to determine the cause. Preliminary findings suggest that this is, according to Dr. Souza, “the result of a natural die off that is being triggered by the increasingly warmer water temperatures.”

He explains, “During a typical winter there is a fair amount of natural fish mortality. We rarely see the effects of this as the dead fish settle to the bottom of the lake and slowly decompose over the winter and early spring. As you are aware, last winter was mild. This probably allowed a lot of the fish that would have succumbed over the winter to survive. However, now that the water is warming and the fish’s metabolic rates are increasing, the fish become excessively traumatized. They can’t cope with the additional physical burden and become more prone to fungal/bacteria infections or simply cannot maintain themselves. Additionally, some of larger dead fish likely died due to post-spawning stresses.”

Water quality is “excellent” according to Dr. Souza and no current conditions have been found that would cause a fish kill.  Dissolved oxygen levels, from the surface to the bottom, are normal and either at or slightly greater than 100% saturation. Though water temperatures are warmer than usual there is no apparent thermal stratification, pH readings are within normal range, and clarity is “outstanding.” There have been no reported spills or any evidence that some type of contaminant is responsible for the fish kill.

Lake treatment over the past month is not considered to be the culprit either. Lake treatments done to date, and the reason for their implementation, are consistent with what has been done in the past and consistent with the management plan developed for the lakes. Furthermore Princeton Hydro has observed similar fish kills in two lakes/ponds in southern New Jersey and neither had been treated with an aquatic pesticide.

Arrangements have been made with Allied Biological to transport fish specimens to a NJDEP laboratory and a lab in Maine for analysis. These fish will be collected on May 29th from all three lakes and shipped overnight to the labs. In a phone conversation with Dr. Souza, the NJDEP biologist also seemed to feel that the die off is a natural occurrence triggered by the additional stresses of spawning and increasing water temperatures.

All further findings from the Club’s consultants and the labs will be shared with Club members as reports become available. For Dr. Souza’s memo, click here.