City officials on Saturday warned people and pets to stay away from Shelley Lake and a creek that flows into it after an apparent chemical spill upstream.
The city posted signs around the lake Saturday, warning that the water might be toxic and that fishing, swimming or drinking, even by pets, were prohibited.
The city also moved a planned fishing tournament Saturday from Shelley Lake to Eastgate Park.
City officials think that someone dumped some sort of organic compound into a storm drain that leads into a creek upstream of the lake, City Manager Russell Allen said Saturday. Neighbors complained of a petroleum smell, and parks employees reported dead fish in the stream, Allen said.
"We don't have any evidence that it got down to Shelley Lake," he said. "But until we identify what it was, the source of it, we're trying to be particularly cautious."