GILMER, Texas—Fisherman who like catching big mouth bass in Caddo Lake are being warned not to eat too many of them.

Matt Chumchal, assistant professor of Biology at Texas Christian University in Fort Worth, addressed the Northeast Texas Regional Water Planning Group during their Wednesday meeting about mercury levels in Caddo Lake.

Chumchal, who has been researching mercury levels in the lake for the past three years, told the group that mercury in water is a global issue and its sources are both natural and man-made.

While Chumchal said most lakes contain ...