The Cape Fear River Watch has closed the Greenfield Lake Boathouse temporarily after hundreds of dead fish were found over the weekend, per the Cape Fear River Watch.
According to CFRW Water Quality Program Manager Rob Clark, people complained about the dead fish over the weekend and that hundreds of dead fish were found at the public boat ramp of different species and sizes.
Clark says that a crew sampled water and found extremely low levels of dissolved oxygen.
Colleen Brown who is a PhD student at UNCW in the aquatic ecology laboratory says they found oxygen levels as low as 5% in the area where the fish were found.
“Nothing can live in 5% oxygen. That’s when water is what’s termed ‘anoxic.’ Basically, not conducive to any life. Nothing can live in there. And that’s why we saw tons of fish everywhere,” Brown said.
However, researchers are still working to find out what exactly caused those low levels of oxygen.
“There are many different things that could have been contributing to it from the runoff from storms from sediments in the lake...It’s springtime, there’s lots of fertilizer. There are so many different aspects of what could have happened to drive this low oxygen level. It could have been an algal bloom that happened and died, and then when algal blooms die they absorb a lot of oxygen,” said Brown.
The city recently did an algae removal. Brown says while that’s not the definitive cause, it could be a piece of the puzzle.
The city helped clean up the dead fish, and it is not known if this is ongoing or a one-time event.
“Preliminary indications are that low dissolved oxygen levels in Greenfield Lake led to a localized die-off of certain fish at Greenfield Lake. The city is working with Cape Fear River Watch and UNC-Wilmington scientists to analyze water conditions and take corrective measures to prevent similar occurrences in the future. City staff are working to clean the lake. Boat rentals are temporarily suspended during the cleanup,” a spokesperson with the city sent to WECT.
Clark says an algal bloom is the most likely cause for these low oxygen levels.
Clark explains that algal blooms are caused by excess nutrients from fertilizers, wastewater, or stormwater runoff.
“The excess nutrients in the lake are a large issue. And I think a lot of people are aware of that. And I think it’s important also to acknowledge what we do upstream can affect downstream.”
Clark says there are toxic and non-toxic algal blooms. The samples from the water currently are coming up as non-toxic.
“That’s not to say we’re in the clear. That’s one little sample from this sub-sample of water. We’re going to look at the water sample under the microscope to see what species of algae are in this water and send it to another lab at UNCW to determine what other species are in here,” said Brown.
Brown says for now, people and pets should stay out of the lake.
Copyright 2024 WECT. All rights reserved.
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