The Glenn-Colusa Irrigation District fish screen consists of 40 screen drums, each 17-ft in diameter and 8 ft wide, arranged in a linear configuration along a dredged side channel of the Sacramento River, and having a total capacity of 3,000 ft3/s. The original purpose of the Glenn-Colusa fish screen was to protect migrating juvenile chinook salmon Oncorhynchus tshawytscha as they moved downstream. The screens have proven troublesome because of changes in water surface elevation and profile brought about by erosion and siltation in the river channel during heavy winter storms. Effective screen area and bypass flows have been substantially reduced. Currently, a single 17-ft prototype drum is being tested. It has been retrofitted with profile-wire screen with 3/32-in slots versus wire mesh of 4-by-4 (wires per inch) stainless steel.