ARLINGTON (CBSDFW.COM) – Homeowners in one Arlington neighborhood are wondering what could have killed hundreds of fish in a creak near their homes. Was it the chemical runoff from yards, someone spraying for mosquitos, or a side effect from natural gas drilling?

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One Fish Creek resident says she made the discovery when she came to the creek Wednesday afternoon. The dead fish were found along about a mile stretch of the creek.

“I hope its not gas drilling related. There (is) so much gas drilling around us. That was my first fear,” she said.

She also noticed oily patches and white foam on the water’s surface.

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The City of Arlington sent in environmental crews to test for ammonia, chlorine, copper and chemical bonding agents. The city says all the tests came back negative.

Matt Young, Arlington’s Assistant Parks Director, says he believes the water source is safe. “Our environmental staff continues to check and has gone to check every single point of entry on both sides of this corridor for miles upstream and haven’t been able to find anything to this point.”

The city believes the fish deaths are natural.

“We see this on a regular basis,” says Young. “A lot of times temperature and environment change depletes oxygen source. So when it drops from 106 to 80 in a short amount of time, sometimes its difficult for certain types of fish and size of fish to adapt.”

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But some residents are not buying that assessment, and believe more tests are necessary.