Habitat
Sea lampreys prefer to live in calm aquatic environments with
no water obstructions such as dams or waterfalls. They also
thrive in clean areas that are suitable for spawning and
waterways with many fish to serve as hosts. Sea lampreys are
widely distributed along the Northern Atlantic coast of North
America as well as within Atlantic drainages of North America.
They can be found between depths of 0 to 200 meters in both
fresh and saltwater environments (Beamish,1980). During the sea
lampreys free swimming stage, sea lamprey are seen off the
coast of the United States in the Atlantic Ocean. They can be
found as far north as Labrador and as far south as Florida. Sea
lampreys are found in highest densities between the latitudes of
30-53º (Beamish,1980). These latitudes are suitable for sea
lamprey because they tend to migrate to warmer waters when
temperatures get cooler. 
The sea lamprey’s habitat ties closely with its reproductive cycle. In the spring, sea lamprey migrate into freshwater streams with gravel bottoms to build nests and reproduce. Once the larval ammocoetes hatch, they float down stream and burrow into the bottoms and banks of rivers, where they filter feed. The ammocoetes remain dormant in this habitat for three to four years until they migrate back to the coast of the United States to begin the free swimming adult stage (Cherry, 2011).
Although sea lampreys are native to the Atlantic Ocean, these
creatures have been seen throughout the Great Lakes region. How did
they get there you ask? It has been reported that sea lamprey
invaded the Great Lakes region through various shipping canals.
These sea lampreys have adapted to live solely in freshwater
environments without needing to return to the Atlantic coast of
North America (Morman et al. 1980).
For more information on habitat visit Animal Divesity Web.