Because Saginaw Bay is shallower and warmer than the main basin of Lake Huron, its fish community is also different. Both recreational and commercial fisheries operate in Saginaw Bay. Walleye and yellow perch are the primary sport species while the commercial fishery primarily targets lake whitefish and yellow perch. The commercial fishery is a state of Michigan licensed fishery as opposed to tribal based fisheries that operate in other parts of Lake Huron. The recreational fishery became more prominent in the last half of the 20th century. Prior to that, the bay's fisheries were almost entirely commercial. Like much of the Great Lakes, the fisheries collapsed or became severely degraded around the middle part of the 20th century. This was attributed mainly to habitat degradation (dam construction, sedimentation of off shore spawning areas), pollution, cultural eutrophication, and the effects of invasive species. The relatively intense exploitation of the commercial fisheries that operated at the time probably hastened the declines but was not believed to be the main cause since they had operated there since the late 17th century.