The islands are drained by a number of small, mostly unnamed streams with drainage areas generally less than five square miles.
Streams typically are dry in the summer.
Numerous small lakes, ponds, pits and reservoirs occur on the islands and are sources of water for drinking, stock watering and irrigation. Ground water provides most of the drinking water in the islands. Productive sand and gravel aquifers exist on Lopez Island but most wells obtain water from less productive bedrock aquifers. List Decision Matrix identifies five impaired marine water bodies. All listings with the exception of one, dissolved oxygen at Eastsound, are proposed for removal from the list.