The barrier is a temporary structure that is installed each March, during the sea lamprey spawning run, and then removed a couple months later when spawning sea lamprey are no longer present.
Sea lamprey are a parasitic invasive species that prey on sportfish by latching onto a host and sucking their blood and other bodily fluids. This seasonally-operated barrier blocks sea lamprey from reaching spawning habitat in Orwell Brook and reduces the amount of chemical treatment needed to keep the population under control.
More information about the sea lamprey control program in the Great Lakes can be found on the Great Lakes Fisheries Commission website.
Photo of Orwell Brook sea lamprey barrier courtesy DEC.