ALT A rainbow trout rests among cobble substrate in Panther Creek.

ALT Map of the conterminous United States (lower 48 states) with hydrologic units color-coded by level of water limitation. The legend to the right of the map explains that levels of water limitation include very low (deep blue), low (blue gray), moderate (tan), high (mustard yellow), and severe (light yellow). Hydrologic units with very low or no water limitation appear clustered in northwestern and northeastern areas of the U.S., as well as around the Great Lakes and down the Appalachian Mountains. Hydrologic units with high or severe water limitation appear clustered in the Central Valley of California and the southwest and south-central areas of the U.S.