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KANSAS CITY, Mo. — Missouri’s Department of Conservation said more than 50,000 fish died in a fish kill in Brush Creek over the past week.

State researchers tested the water in Brush Creek as part of its investigation into the problem, but believe it happened naturally. They said thousands of carp and sunfish were found in a four-mile stretch of Brush Creek between the Country Club Plaza and Elmwood Avenue.

Biologists believe recent heavy rain raised the water levels and caused the carp to swim upstream into the pond. When the water level dropped, the fish couldn’t swim back out and into the Blue River. Biologists also pointed out there are concrete structures in the creek. They say the concrete can cause stagnant water that has higher temperatures and low oxygen levels. That mix can also cause fish to die.

People who live and work in the area contacted FOX4 Problem Solvers earlier this week after seeing and smelling hundreds of dead fish in the water.

Kansas City, Missouri said it hired a contractor to clean up the problem. Crews walked in the shallow part of the water Wednesday afternoon scooping the dead fish out of the water.

The city’s Public Works Department said it knew about the dead fish problem on Monday but had to wait for tests to be run.

The Missouri Department of Conservation said it handled about 200 fish kills and other similar issues ever year.