 The remaining bitumen can make cleaning up a dilbit spill more difficult than a conventional oil spill, particularly if dredging is considered too ecologically damaging.During the 2010 Kalamazoo River oil spill, the heavier components combined with silt and sank to the bottom of the water column, making cleanup difficult.Cleanup of the spill was still underway three years after the event, and officials at the Michigan Department of Natural Resources' Fishery Division stated that it will "be many more years before the agency can measure the full impact on fish and other animals' reproductive cycles."