U.S. Fish & Wildlife Service


Hydrology of Alaska

Alaska's abundance of rivers, lakes, wetlands, snowfields, and glaciers comprise an estimated 40 percent of the Nation's surface water. There are more than 12,000 rivers in Alaska, and three of those rivers, the Yukon, the Kuskokwim, and the Copper, are among the ten largest rivers in the United States. Alaska has more than 3 million lakes ranging from pond size to 1,000 square miles. Despite Alaska's wealth of water, its water resources are not uniformly distributed geographically or seasonally. Annual precipitation ranges from an average of five inches on the Arctic Slope to an average of 300 inches in the maritime rain forests of Southeast Alaska. Glaciers and icefields cover about 5 percent and permafrost underlies approximately 85 percent of Alaska, which affect the timing and quantity of runoff. Many rivers are affected by ice-jam flooding during spring breakup, and many are ice covered much of the year.

Alaska's Wetland Characteristics 

Old Chevak Wetlands

Old Chevak Wetlands


Most regions of Alaska have a land surface that includes extensive areas of wetlands. Treeless expanses of moist and wet tundra underlain by permafrost occur in the northern and western portions. Interior Alaska contains millions of acres of black spruce muskeg and floodplain wetlands dominated by deciduous shrubs and emergents. Shrub and herbaceous bogs are a predominant feature of the landscape in southcentral and southeast Alaska. In mountainous areas such as the Brooks or Alaska Ranges, wetlands have developed in drainages and on vegetated slopes. Some of the nation’s most extensive complexes of salt marshes and mud flats occur along the coasts of the Beaufort, Chukchi, and Bering Seas, and the Gulf of Alaska.

Wetlands are abundant in the valleys and basins associated with large river systems including the Yukon, Kuskokwim, Porcupine, Tanana, and Koyukuk Rivers. Significant wetland areas also occur on the major river deltas in Alaska. The Yukon-Kuskokwim Delta, one of the world’s largest coastal deltaic formations, supports a variety of wetland types including wet tundra, grassy sloughs, shrub swamps, ponds and brackish marsh. Other major deltas in Alaska that are predominantly wetland are the Colville River Delta on the Beaufort Sea coast, the Copper River Delta in southcentral Alaska, and the Stikine River Delta in the southeast region.

Inventory Maps

2013 NWI Mapping Status: Alaska Region

The Alaska National Wetlands Inventory (AK NWI) is responsible for mapping Alaska’s wetland habitats. Guided by our overall national strategy, the AK NWI conducts strategic mapping of high priority wetland habitats, carries out status and trends analyses of wetlands and other aquatic habitats, and identifies and assesses threats to aquatic habitats at risk. Currently, 43 percent of Alaska has been mapped, and 36 percent has been digitized.

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Water Resources

Testing the water in a small creek

The Water Resources Branch collects streamflow and water quality data within national wildlife refuges of Alaska to protect fish and wildlife habitat and the natural biodiversity of aquatic resources. The branch also provides technical assistance to other programs within the Fish and Wildlife Service.

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Ecology Group & Natural Resources

Moose feeding in Innoko NWR, Photo Credit: Kate Banish/USFWS

The Ecology group provides scientific leadership and technical assistance to refuge biology programs. This program coordinates refuge biological programs regionally, conducts biological reviews of refuge programs, provides biometric expertise, and conducts botanical surveys on refuges. 

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