Sea lamprey (Petromyzon marinus) are parasitic fish not-native to the Great Lakes. Sea lamprey parasitize other fish by sucking their blood and other body fluids. Sea lampreys are unique from many other fishes in that they do not have jaws or other bony structures, and instead possess a skeleton made of cartilage. While sea lamprey resemble eels, they are not related and are set apart by their unique mouth: a large oral sucking disk filled with sharp, horn-shaped teeth surrounding a sharp rasping tongue.

There are four native lamprey species in the Great Lakes: the American brook, northern brook, silver and chestnut lamprey. All of the native lamprey species are much smaller than sea lamprey and are part of a balanced fish community. The largest of the native lamprey is the silver lamprey, which only reaches about half the size of an adult sea lamprey.

Of the native lamprey species, only two are parasitic: the chestnut and silver lamprey. The silver and chestnut lamprey have a similar life cycle as sea lamprey – the big difference is that, as parasites, silver and chestnut lamprey typically do not kill their fish hosts. Thus, unlike sea lampreys, which are considered both parasites and predators, the native lamprey species are only considered parasites.

The other two native lamprey species, the American brook and northern brook (the “brook” species), are non-parasitic. The brook species experience a metamorphosis similar to the parasitic species (developing eyes, fins, and a toothed mouth); however, the non-parasitic species skip the parasitic phase and instead immediately spawn after metamorphosis. The non-parasitic “brook” lamprey spend their entire life cycle in streams.

Sea lamprey attach to fish with their suction cup mouths then attach their teeth into flesh. Once securely attached, sea lampreys rasp through the fish’s scales and skin with their sharp tongue. Sea lamprey feed on the fish’s body fluids by secreting an enzyme that prevents blood from clotting, similar to how a leech feeds off its host. Sea lamprey are native to the Atlantic Ocean and invaded the Great Lakes in the early 20^th century. In the Great Lakes, they are predators, with each individual capable of killing up to 40 pounds of fish over their 12-18 month feeding period. Only one in seven fish attacked by a sea lamprey will survive, either dying directly from the attack or from infections in the wound after the initial attack. Sea lampreys entered Lake Michigan around 1936 and subsequently infested several tributaries of the lower Grand River.

Sea lamprey spawn in streams, and their larvae live in those streams before they become parasitic. Sea lamprey control depends on a targeted  lampricide to kill the larvae or, in stream systems that are large (like the Grand River and its tributaries), barriers to prevent sea lamprey access to their spawning grounds.

How do we block sea lamprey but still provide passage for native and desirable fish species? This is a question plaguing the resource management agencies as conversations about removing aging dams/barriers and restoring connectivity are increasing across the country. There are options available to control sea lamprey but they must be evaluated on a case-by-case basis.

The Great Lakes Fishery Commission is leading the design and permitting effort for the upper reach project and has contracted with the U.S. Army Corps of Engineers to conduct an Environmental Impact Statement process that kicked off in April of 2019. 14 design alternatives have been developed for the upper reach where sea lamprey control will be evaluated and will undergo additional evaluation of impacts and feasibility through the EIS process. In 2021, the GLFC put the EIS process on hold until the permit for the Lower Reach project was near complete to avoid duplication of work. Once the EIS process resumes, additional analysis on the 14 alternatives, including the proposed Adjustable Hydraulic Structure (ASH) as proposed by the City and GRWW will commence.

The proposed Adjustable Hydraulic Structure (AHS) is a uniquely designed barrier that could replace the Sixth Street Dam as the primary sea lamprey barrier on the river. The AHS structure has been proposed to be constructed approximately one mile upstream of the Sixth Street Dam. Sea lamprey escapement, upstream of the project site, would have a significant impact on the Lake Michigan fishery. The AHS is designed to ensure sea lampreys do not migrate upstream of the City of Grand Rapids. This structure would deny sea lampreys access to more than 1,900 miles of stream habitat, which would otherwise cost the Great Lakes Fishery Commission between $1.2 million and $1.8 million annually to treat with lampricides. An effective lamprey barrier structure on the Grand River is critical given that just one sea lamprey escapement event upstream of Grand Rapids could inflict millions of dollars in economic loss. The AHS is one alternative being evaluated for feasibility through the Environmental Impact Statement process being led by the Great Lakes Fishery Commission.

The proposed adjustable hydraulic structure (AHS) has been uniquely designed to maintain blockage to the upstream migration of sea lamprey. It would utilize inflatable bladders to raise and lower steel gates to maintain sea lamprey blockage criteria established  by the Great Lakes Fisheries Commission. During times when the gates must be lowered to accommodate high flow events, the AHS relies on faster water velocities to prevent upstream sea lamprey migration.

The operational functionality of the AHS would be able to achieve multiple goals, including flood conveyance, sea lamprey control, maintaining target upstream water levels, and potentially allowing upstream fish passage during periods when sea lamprey are not in the river.

Yes. If permitted access to the upper Grand River, a relatively small number of sea lampreys could produce between 135,000 and 200,000 parasitic juvenile sea lamprey. Such an event could result in the loss of almost two million fish with an economic value of about $39-$58 million. Lampricide treatment efficiency for the Grand River is estimated at 95% due to the nature of the watershed, so there will still be considerable economic loss under a treatment scenario. Applying a 95% treatment efficiency would still result in an annual production of 6,750-10,000 juveniles to Lake Michigan and an economic cost of $1,950,000 – $2,900,000 annually.

The City and GRWW recognized early on the need for fish passage around the AHS when it is being operated as a sea lamprey barrier. A fish passage ladder, similar in function to the existing structure at the Sixth Street Dam, would likely be incorporated into the proposed AHS structure and would create similar passage conditions while maintaining effectiveness as a sea lamprey barrier. The design of the AHS was shared with the Great Lakes Fishery Commission and is one of 14 alternatives that will be considered as part of the Upper Reach Project which will ultimately be selected by the Great Lakes Fishery Commission. 

Recognizing the future desires for a water trail and increased opportunities for non-motorized watercraft on the Grand River, a small craft portage was also incorporated into the design of the potential AHS to allow passage around the structure.