Large fish nest in lower right corner. Most likely made by a Bass.
Bass making a nest.
kickinbass FC youtube.com
When water temperatures reach 60 F / 15.6 C male fish makes beds or nest at depths of 12 to 18 inches / 30cm. deeper when water gets warmer.
Females then show up to drop their eggs. Males will hit the females on their sides to shake loose the eggs.
Female leaves as soon as eggs are dropped, while male sticks around to guard the nest.
source
bassmaster.com