The mercury issue is not unique to the Ohio River. It occurs in all rivers. The issue arrises from mercury retention in tissues. This is compounded by "big fish eats smaller fish". The mercury stored in small fish is passed on to the larger fish and so on. The older the big fish, the more mercury it will have. By the time a fish is large enough for human consumption, it hasn't accumulated enough mercury for the fish to suffer from it. However, there is enough to warrant warnings about their consumption.
Wood does not experience this problem. Just for piece of mind, you can still soak it in tap water several times. A salt soak will kill any parasites that may be riding in the cracks and crevices.