Elevated levels of mercury found in large walleyes in Newell Lake are prompting the state to warn people to limit their consumption of the fish taken from the lake.
Most states have mercury advisories, often in many more lakes than have made the list in South Dakota. Currently, the state has nine. Environmental specialists have found mercury in fish tissue below the warning level of 1 part per million at most lakes tested across the state. Though the state sets the warning level at 1 ppm, it is considering a recommendation to lower that limit to 0.3 ppm.
The fish with the highest mercury levels in Newell Lake were walleyes 18 inches and longer, so the advisory applies to walleyes of that size. State Game, Fish & Parks Department regional fisheries manager Gene Galinat of Rapid City said the advisory isn’t likely to have a great impact on sport fishing or fish consumption, since walleyes of that size are not abundant or easily caught there.
“We don’t see a lot of walleyes in that lake of that size,” he said.
Newell Lake does have a healthy bluegill population. That species is lower on the food chain and less likely to concentrate mercury to problem levels, Galinat said.
Most other lakes in the Black Hills show some level of mercury in the tissue of larger predator fish, but typically they are well below the 1 ppm limit. Fish in some, such as Angostura Reservoir near Hot Springs, have barely registered mercury in sampled tissue.
Belle Fourche Reservoir, another large irrigation reservoir near Belle Fourche, had low readings in the 0.05 range for walleyes, although there were higher readings still below the limit in large catfish. The other three West River lakes on the mercury advisory list are for familiar culprits for concentrating the metal: larger predator fish.
The advisory on 81-acre Lake Isabel was issued in November of 2002 and is for largemouth bass 17 inches and longer and northern pike 25 inches and longer. Bass readings there went up to 1.62 ppm. On 112-acre Pudwell Dam, the advisory issued in August 2008 is for walleyes. Walleye readings there went up to 1.23 ppm. And the advisory on 65-acre Roosevelt Lake issued in February of 2004 covers largemouth bass 18 inches and longer. Readings there reached 1.11 ppm.