Downstream of the refuge, the river flows roughly parallel to U.S. Route 97, receiving Spring Creek from the right at Collier Memorial State Park, about 5 miles (8.0 km) north of Chiloquin.

[5] The Williamson is known for especially large wild Great Basin redband trout, which move into the river to spawn and to escape Upper Klamath Lake when it gets warm.

[4] Since 2003, The Nature Conservancy and other organizations have been working to restore about 12 square miles (31 km2) of wetlands in the Williamson River delta at the north end of Upper Klamath Lake.

Formerly diked and drained for farming, the delta provides habitat for millions of migrating birds as well as many native species of fish, mollusks, and aquatic plants.

The eruption of Mount Mazama about 7,700 years ago contributed an enormous amount of sediment to the lake and marsh basins, and filled the canyon of the Williamson River.