Have you ever watched a nature special on the great migrations of the Serengeti or the long-distanced flights of migratory birds? In the rivers and streams right next to the path you’re walking on, or the office window you’re daydreaming out of, there are great underwater migrations occurring every day! River herring adults are returning to ponds and stream sides to spawn and lay eggs; striped bass are right at their heels looking for their next meal; and white suckers are making their journeys from breeding grounds to feeding grounds. Most unusual of all, the American Eel is making a reverse migration from its adult home in freshwater streams and rivers to the middle of the Atlantic Ocean. Some of the greatest spectacles are happening right in our backyard, including the Charles River. We just need to stop and take a look!
And just like other great migrations, some of these mass movements have been impacted and threatened by human activity. Just as fences can restrict movements of deer and antelope, dams and culverts create barriers to movement, and are partly responsible for some of the drastic decreases in migratory fish movements. Water use in surrounding communities also affects the levels of water in the river, at times of very low flow sections of rivers can be cut-off and create another barrier to migration.