I used to do canoe trips on the English River, in western Ontario. One of the mills polluted the river with mercury, and it made the fish poisonous to eat in quantity. Throughout the lakes downstream there were signs giving the allowable eating -- on the order of one trout per week. We could drink the water. Local indians at the Grassy Narrows reserve drank the water year round. But the fish were off limits, creating severe hardship for the indians, both from a loss of an important food source, and from guiding tourist fishermen.
Methylmercury accumulates up the food chain. Bass are tertiary feeders, eating the bugs that eat the plankton. So you shouldn't eat the bass.
But the bass are still doing quite well. The Osprey that munch on bass may have problems.
I'm surprised that there is only a factor of 50 difference between the levels in the water and in the bass. Usually there is about a factor of 10 increase in concentration at each level of the food chain. I'd expect the difference to be between 1000 and 10,000 times. One source claims a food chain concentration of a million times for top predators. You may want to verify that water level. Could it be parts per billion instead of parts per million?
If your figures for the concentration in the water are correct, they are a factor of 20 higher than Liam's figures. This is still reasonably safe for occasional visits -- a week canoeing each summer -- but not a good idea if you live there.
claims that mercury will be removed by an activated charcoal filter or by starch xanthate. Activated charcoal filters are commonly used to remove H2S from water. (rotten egg smell)