Sea lampreys enter the Grand River from Lake Michigan and inhabit the river downstream of the Sixth Street Dam. That stretch of the river contains poor sea lamprey habitat and the stretch is not productive enough to warrant treatments in the Grand itself. Crockery and Norris creeks, located downstream of the Sixth Street Dam, are treated regularly. The upper Grand River and its tributaries have been regularly surveyed for sea lampreys since 1962. A total of 44 tributaries upstream of the Sixth Street Dam have been surveyed. Harmless, native lampreys are also known to occupy reaches of the watershed upstream of the Sixth Street Dam.
Two previous sea lamprey escapement events have been noted upstream of the Sixth Street Dam. Larval sea lampreys were collected from Lowell Creek in 1962 and the stream was treated with TFM (3-trifluoromethyl-4'-nitrophenol) in 1965. Larval sea lampreys were collected from the Rogue River during 2008, resulting in a treatment in 2009. The source(s) of escapement for each event is unknown.
Recent larval assessment sampling in 2022 identified several large sea lamprey larvae in the Rogue River likely a result of flooding in the spring of 2020 when the Sixth Street Dam was submerged with high water. Additional evaluation and assessment of this finding, and the need for a lampricide treatment, is currently underway with the U.S. Fish and Wildlife Service Sea Lamprey Control Program and Great Lakes Fishery Commision.