Largest Reservoirs in Washington

Washington has 802 dams with recorded storage capacity. The largest is Grand Coulee Dam with 9,715,346 acre-feet of maximum storage. One acre-foot equals about 326,000 gallons — enough to supply roughly two households for a year.

#	Dam	County	Max Storage (acre-ft)	Height (ft)	Purpose	Year
1	Grand Coulee Dam	Okanogan	9,715,346	550	Flood Risk Reduction	1941
2	Mossyrock	Lewis	1,900,000	606	Hydroelectric	1968
3	Ross	Whatcom	1,452,750	540	Hydroelectric	1949
4	North Dam	Grant	1,275,000	145	Flood Risk Reduction	1951
5	Dry Falls Dam	Grant	1,275,000	123	Flood Risk Reduction	1949
6	Wanapum	Kittitas	796,000	206	Hydroelectric	1965
7	Swift No. 1	Skamania	755,500	412	Hydroelectric	1958
8	Chief Joseph Dam	Douglas	593,000	230	Hydroelectric	1955
9	Little Goose Lock And Dam	Columbia	565,200	226	Navigation	1970
10	O'sullivan Dam	Grant	546,300	200	Flood Risk Reduction	1949
11	Wells	Chelan	500,000	160	Hydroelectric	1968
12	Cushman No 1	Mason	482,757	272	Hydroelectric	1926
13	Hiram M. Chittenden Locks And Dam	King	458,000	63	Navigation	1916
14	Cle Elum Dike 2	Kittitas	437,000	13		1933
15	Lower Monumental Lock And Dam	Franklin	432,000	226	Navigation	1969
16	Merwin	Cowlitz	422,000	313	Hydroelectric	1931
17	Yale	Cowlitz	402,000	323	Hydroelectric	1953
18	Yale Saddle Dam	Cowlitz	402,000	40	Hydroelectric	1953
19	Rocky Reach	Chelan	390,000	130	Hydroelectric	1962
20	Alder	Pierce	241,195	330	Hydroelectric	1945
21	Kachess Dam	Kittitas	239,000	115	Flood Risk Reduction	1912
22	Tieton Dam	Yakima	198,000	319	Flood Risk Reduction	1925
23	Culmback	Snohomish	193,440	262	Hydroelectric	1983
24	Priest Rapids	Grant	191,000	187	Hydroelectric	1961
25	Mayfield	Lewis	184,194	250	Hydroelectric	1963
26	Masonry Dam	King	175,000	230	Hydroelectric	1914
27	Keechelus Dam	Kittitas	158,000	128	Flood Risk Reduction	1917
28	Lower Baker	Skagit	146,279	285	Hydroelectric	1927
29	Howard A. Hanson Dam	King	136,700	235	Flood Risk Reduction	1962
30	Rock Island	Douglas	131,000	71	Hydroelectric	1932
31	Mud Mountain Dam	King	106,000	425	Flood Risk Reduction	1948
32	Boundary	Pend Oreille	95,000	360	Hydroelectric	1967
33	Diablo	Whatcom	89,200	389	Hydroelectric	1929
34	Coldwater Debris Dam	Cowlitz	78,700	200	Other	1981
35	Zosel Dam	Okanogan	77,298	16	Irrigation	1986
36	Pinto Dam	Grant	76,500	130	Flood Risk Reduction	1948
37	Wynoochee	Grays Harbor	76,000	175	Water Supply	1972
38	Morse Lake Overflow Dike	King	75,000	30	Water Supply	1904
39	Whatcom Lake Dam	Whatcom	70,000	19	Recreation	1937
40	Tolt River - South Fork	King	68,400	200	Water Supply	1962
41	Spirit Lake Outlet Tunnel	Skamania	57,000	184	Flood Risk Reduction	1985
42	Tapps Lake Dike No 2a	Pierce	53,600	9	Recreation	1911
43	Tapps Lake Dike No10	Pierce	53,600	18	Recreation	1911
44	Tapps Lake Dike No 6	Pierce	53,600	28	Recreation	1911
45	Tapps Lake Dike No 9	Pierce	53,600	15	Recreation	1911
46	Tapps Lake Dike No 4	Pierce	53,600	48	Recreation	1911
47	Tapps Lake Dike No 12	Pierce	53,600	14	Recreation	1911
48	Tapps Lake Dike No 2b	Pierce	53,600	15	Recreation	1911
49	Tapps Lake Dike No 3	Pierce	53,600	15	Recreation	1911
50	Tapps Lake Dike No 5	Pierce	53,600	28	Recreation	1911

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