The Bear River Bird Refuge (Box Elder) is located in the northern section of the Great Salt Lake, 15 miles (24.14 km) west of Brigham City. In 1903 Settlers moved into the area diverting large amounts of Bear River water for upstream use causing the mashes to dry up and leaving only about three thousand of the original forty-five thousand wetland acres. Avian botulism claimed hundreds of thousands of birds. Congress soon passed an act making the area a National Wildlife Refuge. Today it is a water management system at the mouth of the Bear River and includes 105 miles of canals and dikes and over 54 control structures. Five 5000 acre impoundments are created by the dykes. The average depth of the water is only about 12 inches. The refuge supplies food for migrating birds in the open water areas while abundant accompanying marshes provide excellent nesting and brood rearing habitat.