The 25,500-acre (10,300 ha) Yolo Bypass protects Sacramento and other California Central Valley communities from flooding.
 During wet seasons, it can be full of water.
It contains the Vic Fazio Yolo Wildlife Area, the largest ecological restoration project west of the Everglades.
Other nature preserves in it include the Fremont Weir Wildlife Area and Yolo Bypass Wildlife Area.

The Yolo Bypass begins at the Fremont Weir Wildlife Area, located approximately 15 miles (24 km) northwest of Sacramento and lying south of the Sacramento River, upstream from its confluence with the Feather River.
When seasonal rains cause the river to rise, water is diverted via the concrete Fremont Weir into the Yolo Bypass floodplain.
The Yolo Bypass can carry up to five times the capacity of the Sacramento River, preventing it from flooding Sacramento.
The diverted water re-enters the Sacramento River delta near Rio Vista.
A 2002 study showed that water begins to flow from the Sacramento into the Fremont Weir when the flow reaches approximately 2,000 cubic metres per second (4,200,000 cu ft/min); for comparison, the capacity of the Yolo Bypass is 14,000 to 15,000 cubic metres per second (30,000,000 to 32,000,000 cu ft/min).

Approximately 250,000 Mexican free-tailed bats migrate to the Yolo Causeway every June.
They roost in the expansion joints between the causeway segments, and feed on the insects that live in the wetlands formed by the Yolo Bypass.
The 25,500-acre (10,300 ha) Yolo Bypass protects Sacramento and other California Central Valley communities from flooding.  During wet seasons, it can be full of water. It contains the Vic Fazio Yolo Wildlife Area, the largest ecological restoration project west of the Everglades. Other nature preserves in it include the Fremont Weir Wildlife Area and Yolo Bypass Wildlife Area.
The Yolo Bypass begins at the Fremont Weir Wildlife Area, located approximately 15 miles (24 km) northwest of Sacramento and lying south of the Sacramento River, upstream from its confluence with the Feather River. When seasonal rains cause the river to rise, water is diverted via the concrete Fremont Weir into the Yolo Bypass floodplain. The Yolo Bypass can carry up to five times the capacity of the Sacramento River, preventing it from flooding Sacramento. The diverted water re-enters the Sacramento River delta near Rio Vista. A 2002 study showed that water begins to flow from the Sacramento into the Fremont Weir when the flow reaches approximately 2,000 cubic metres per second (4,200,000 cu ft/min); for comparison, the capacity of the Yolo Bypass is 14,000 to 15,000 cubic metres per second (30,000,000 to 32,000,000 cu ft/min).
Approximately 250,000 Mexican free-tailed bats migrate to the Yolo Causeway every June. They roost in the expansion joints between the causeway segments, and feed on the insects that live in the wetlands formed by the Yolo Bypass.
Yolo Causeway