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A mysterious and unusual early-season fish kill manifested itself in Rehoboth Beach’s Silver Lake Saturday afternoon, April 26. The kill “decimated” the lake’s fish population according to Delaware’s Department of Natural Resources and Environmental Control Secretary John Hughes.
A resident of Rehoboth Beach, Hughes made his way to the lake soon after reports of the problem came into the state. “I use the term decimate because in ancient Roman times a system of execution involved killing every 10th man as a form of punishment in an unruly community. In this case though, it looks like a lot more than one in 10 fish have died.” Hughes said the number of dead fish, including gizzard shad, blue gills, carp and large-mouth bass, easily reaches into the thousands.
Loss of many mature large-mouth bass is particularly disturbing to Delaware’s Fisheries Division Director Roy Miller who also responded to the scene early with Hughes. “These are trophy fish that would have been a lifetime catch for any child fishing in Silver Lake,” said Miller. “It takes 10 years for bass to reach this size and now they’re gone.” He took a close look at four exceptionally large bass that he pulled onto the grass near the northwestern end of the pond. The largest was 21.5 inches long and weighed an estimated seven pounds. “I’d say it’s a female and full of eggs,” said Miller. “I think at least three of them are females with eggs and the other a male.”
While Miller examined the dead fish, other large-mouth bass of comparable size could be seen working their way toward the edge of the lake trying to find oxygen.
Miller said preliminary analysis showed ultra-low oxygen levels as the culprit in the fish kill. “The northwestern end is the worst. We found oxygen levels there of one part per million and less. Anytime you get less than two parts per million the system is stressed and can’t sustain fish life. A healthy system is above six and seven parts per millions of oxygen. Out toward the Silver Lake Bridge, we found two and three parts per million which is better than the northwestern end but still not enough to sustain life.”
Hughes said a detailed laboratory analysis of the water would be made to determine what happened to deplete the oxygen. “That takes some time, but I want to find out what happened. Fish kills like this usually happen later in the season when temperatures are warmer. Algae blooms, feeding on nutrients in the lake bottom – from fertilizer and waterfowl droppings, use up oxygen rapidly and can lead to kills. But this is early. I’ve been speculating. It’s been relatively calm, wind-wise for a few days, and there’s a tremendous amount of pollen around. You can see sheen on the water from the pollen. Maybe the pollen has capped the pond in a way and because of that and little wind stirring, the water hasn’t been reoxygenated and the fish have used up all that is in it. But I don’t know. Maybe there’s unicellular or algal life that we can’t see. That’s what we hope the analysis will show. We don’t think it’s a toxin – some kind of poison that someone put in the lake – but there has to be some cause.”
Rehoboth Beach Mayor Sam Cooper arrived on the scene and agreed that Rehoboth Beach Fire Company should bring a truck to begin drafting water from the lake and reoxygenating the water. “I don’t know how long the truck can stay on the scene but maybe it will be helpful,” said Cooper as he watched the company’s mini-pumper set up on the edge of the lake and begin spraying.
Hughes also asked DNREC employees to bring other pumps to the scene to begin reoxygenating. Those pumps worked through the night Saturday and into Sunday to try to save what fish remained alive.
Hughes also said rain that started falling Saturday night and continuing into Sunday – and was forecast to continue through Monday – would be helpful. “Rainfall is highly oxygenated,” said Hughes. “A lot of rain has to help.”
A good deal of Rehoboth Beach stormwater drains into Silver Lake. “It’s not an ideal situation,” said Hughes, a former mayor of Rehoboth, “but it has to go somewhere. I’m not sure that the canal or the ocean would be a better solution. Ultimately I would like to see Silver Lake dredged. It’s so shallow now that it heats up quickly and that can cause problems.”
Contact Dennis Forney at dnf@capegazette.com
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