Fish don't need air to survive, but they certainly need oxygen—something that's hard to come by in certain spots of the South River.
There's something taking place in the local waterway known as "hypoxic squeezing," where fish are forced to occupy smaller and smaller living spaces as water becomes increasingly difficult to survive in.
Naval Academy professor Andrew Muller, husband of South River Riverkeeper Diana Muller, said two main factors are forcing fish to live in concentrated depths and in a way, squeezing the fish out of livable spaces. High temperatures in surface waters and spreading algae blooms that "hog oxygen" at the bottom are decreasing the amount of areas fish can actually survive, he said.
"The area of liveable depth is getting squeezed from the top and the bottom," the professor said.
These factors could be a predominant reason as to why, during their survey of the South River last week, the scientists discovered 15 dead Asian carp throughout their morning. An excess of nutrients in the water can also cause fish to die, Muller said.
Later, a local boater even stopped the Riverkeeper to say they found additional dead fish near their pier.
Diana Muller said the phenomenon, known as "fish kills," is when large groupings of fish die because of poor water quality.
At a depth of 6 feet, the scientists found anoxic conditions (severe lack of oxygen). Mix that with warm surface temperatures and fish only have a small area to actually live in, she said.
Warm water and low dissolved-oxygen levels could have been a big reason as to why the fish died, but the Asian carp's mating season also was concluding, so she said it could be a mixture of those two factors.
The smell of a dead fish is never pleasant, but a dead fish doesn't necessarily mean the water isn't safe to swim in for humans, Diana Muller said.