This video by Jason Ching follows a team of researchers with the University of Washington’s Alaska Salmon Program as they track a major salmon migration in Lake Iliamna.

Iliamna is the largest lake in Alaska (larger than 1,600 square miles and deeper than 150 feet in places), and it needs to be in order to hold the incredible amount of migratory salmon that travel to it each year. Researchers monitor the fish that annually travel there for their age, size, and the number of individuals present.

Hint: The last number is a large one!