Zebra mussels and exotic species : hearing before the Subcommittee on Oceanography and Great Lakes, the Subcommittee on Fisheries and Wildlife Conservation and the Environment, and the Subcommittee on Coast Guard and Navigation of the Committee on Merchant Marine and Fisheries, House of Representatives, One Hundred First Congress, second session, on H.R. 4214, a bill to help eliminate the growing threat of the zebra mussel ... to the Great Lakes region, June 14, 1990.