LINCOLN, Neb. -- Run-off from a recent thunderstorm and cloudy skies are blamed for a major fish kill at Wildwood Reservoir near Agnew, according to Mark Porath, a biologist with the Nebraska Game and Parks Commission.

Porath said the reservoir had recently been rehabilitated and had refilled slowly, allowing the establishment of desirable aquatic vegetation and a quickly growing fish population of largemouth bass, bluegill, walleye and channel catfish. The warm sunny weather and excellent water clarity permitted sunlight to reach depths of 6-8 feet, which allowed rooted plants to grow all the way to the surface. The expansive stands of vegetation supplied a tremendous amount of food for the fish population, which responded by producing above average growth and reproduction.

“Run-off from a recent thunderstorm and cloudy skies the past few days were enough to decrease the amount of sunlight penetrating the water and caused a significant die- off of aquatic vegetation and algae,” Porath said. “The decay of plant material takes oxygen out of the water and away from the fish population that relies on it.”

The die-off was reported to Commission staff by an angler who had fished Wildwood successfully earlier in the week, then returned to see numerous dead bass, bluegill and catfish floating along the shoreline.

Oxygen measurements taken midday while the kill was occurring were very low and fish were gasping at the surface.

“Typically, in summer months oxygen levels fluctuate daily with plants producing large amounts of oxygen during daylight hours and dipping drastically during the night as biological processes consume the days production. It is likely that most of the adult fish were killed in this event, however many of the small juvenile fish will survive by breathing in the oxygen rich surface layer,” said Porath. “Its unfortunate because we expected a stellar fishing season next year, now we will have to evaluate the surviving population this fall and adjust our management to get it back on track for the following year.”

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