Two canoes crossing open water between forested points in the Boundary Waters

Updated August 2026

Biggest Lake in Washington: Lake Roosevelt (82,300 acres)

Franklin D. Roosevelt Lake (Lake Roosevelt) is Washington's largest lake per the U.S. Army Corps of Engineers, National Inventory of Dams (Grand Coulee Dam, WA00262); reservoir operated by U.S. Bureau of Reclamation. Below: 50 Washington lakes ranked by surface area.

The largest lake in Washington is Franklin D. Roosevelt Lake (Lake Roosevelt) at 82,300 acres , in Ferry, Lincoln, Okanogan, Stevens, Grant County, according to the U.S. Army Corps of Engineers, National Inventory of Dams (Grand Coulee Dam, WA00262); reservoir operated by U.S. Bureau of Reclamation.

Franklin D. Roosevelt Lake (Lake Roosevelt) isn't in our water-quality index — we grade lakes with enough EPA Water Quality Portal samples to score, which leaves out many large reservoirs and border waters. The ranking below covers the 50 Washington lakes we do grade, led by Banks Lake.

Source: U.S. Army Corps of Engineers, National Inventory of Dams (Grand Coulee Dam, WA00262); reservoir operated by U.S. Bureau of Reclamation (2026-07-30). The table below ranks the Washington lakes in our own index by surface area.

Lakes with area data

27,000

Largest (acres)

2,535

Median of top 50

4/50

Reservoirs (vs natural)

Reading Washington's size profile

Washington's largest lake by surface area is Banks Lake in Grant County, spanning 27,000 acres. Most of Washington's biggest waters are natural basins left by glaciers, with stable shorelines and deep main basins.

Surface area is a poor proxy for water quality on its own — a large lake can hold a clean, deep core and a nutrient-loaded bay at the same time. Each lake below links to its full report card with grade, clarity, depth, and EPA impairment status. Area figures come from state DNR surveys and the USACE National Inventory of Dams; grades come from EPA and state monitoring data.

The 50 biggest lakes in Washington by surface area

#	Lake	County	Surface area	Max depth	Grade
1	Banks Lake	Grant	27,000 acres	-	A
2	Lake Wallula	Walla Walla	26,343 acres	-	NR
3	Lake Washington	King	21,992 acres	-	NR
4	Wanapum Lake	Grant	14,362 acres	-	NR
5	Riffe Lake	Lewis	11,224 acres	-	NR
6	Lake Celilo	Klickitat	8,750 acres	-	NR
7	Lake Pateros	Douglas	8,376 acres	-	NR
8	Rufus Woods Lake	Okanogan	8,270 acres	-	NR
9	Lake Sacajawea	Walla Walla	8,146 acres	-	NR
10	Ozette Lake	Clallam	7,433 acres	-	NR
11	Lake Entiat	Chelan	7,171 acres	-	NR
12	Priest Rapids Lake	Grant	6,387 acres	-	NR
13	Lake Crescent	Clallam	5,022 acres	-	NR
14	Lake Whatcom	Whatcom	4,919 acres	-	NR
15	Long Lake	Spokane	4,862 acres	-	NR
16	Swift Reservoir	Skamania	4,586 acres	-	NR
17	Lake Herbert G West	Franklin	4,273 acres	-	NR
18	Lake Wallula	Franklin	4,188 acres	-	NR
19	Lake Cushman	Mason	4,015 acres	-	NR
20	Lake Merwin	Clark	3,837 acres	-	NR
21	Yale Lake	Clark	3,595 acres	-	NR
22	Omak Lake	Okanogan	3,332 acres	-	NR
23	Rock Island Pool	Douglas	3,281 acres	-	NR
24	Alder Lake	Thurston	2,766 acres	-	NR
25	Debra Jane Lake	Pierce	2,570 acres	-	NR
26	Spirit Lake	Skamania	2,535 acres	-	NR
27	Rimrock Reservoir	Yakima	2,525 acres	-	C
28	Lake Tapps	Pierce	2,444 acres	-	NR
29	Lake Wenatchee	Chelan	2,419 acres	-	NR
30	Sanpoil River Arm	Ferry	2,217 acres	-	NR
31	Rock Lake	Whitman	2,190 acres	-	NR
32	Osoyoos Lake	Okanogan	2,059 acres	-	NR
33	Palmer Lake	Okanogan	2,042 acres	-	NR
34	Mayfield Lake	Lewis	2,021 acres	-	NR
35	Silver Lake	Cowlitz	1,989 acres	-	NR
36	Lake Shannon	Skagit	1,938 acres	-	NR
37	Sprague Lake	Lincoln	1,760 acres	-	NR
38	Chester Morse Lake	King	1,743 acres	-	NR
39	Spada Lake	Snohomish	1,687 acres	-	NR
40	Lenore Lake	Grant	1,406 acres	-	NR
41	Bumping Lake	Yakima	1,354 acres	-	NR
42	Sullivan Lake	Pend Oreille	1,296 acres	-	NR
43	Deer Lake	Stevens	1,146 acres	-	NR
44	Loon Lake	Stevens	1,093 acres	-	NR
45	Newman Lake	Spokane	1,091 acres	-	NR
46	South Fork Tolt Reservoir	King	1,011 acres	-	NR
47	Billy Clapp Lake	Grant	1,010 acres	-	NR
48	Lake Stevens	Snohomish	1,003 acres	-	NR
49	Wynoochee Lake	Grays Harbor	990 acres	-	NR
50	Mason Lake	Mason	977 acres	-	NR

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Frequently Asked Questions

What is the largest lake in Washington?

Franklin D. Roosevelt Lake (Lake Roosevelt), at 82,300 acres, in Ferry, Lincoln, Okanogan, Stevens, Grant County. Source: U.S. Army Corps of Engineers, National Inventory of Dams (Grand Coulee Dam, WA00262); reservoir operated by U.S. Bureau of Reclamation, 2026-07-30.

How is lake surface area measured?

Surface area comes from state DNR lake surveys and, for reservoirs, US Army Corps of Engineers (USACE) National Inventory of Dams records. Area is reported in acres at normal pool level. Reservoirs rise and fall with management and drought, so their listed area is the long-term normal rather than a single-day reading.

Are Washington's largest lakes natural or reservoirs?

Of the top 50 Washington lakes by area, 4 sit on a dammed river (reservoirs) and 46 are natural basins. Glacial states (MN, WI, MI, NY) skew natural; plains and southern states (MO, IA, ND, OH) skew toward reservoirs built for water supply, flood control, and recreation.

Do larger lakes have better water quality?

Not reliably. Quality varies more within a big lake than between lakes — a large lake can have a clean, deep main basin and a murky, algae-prone bay fed by a tributary, so one grade can mask wide swings. Depth, watershed land use, and how fast the lake flushes matter far more than raw surface area.

How big is the typical Washington lake in this ranking?

Across the top 50 Washington lakes by surface area, the median is 2,535 acres (Spirit Lake). This list is biased toward the biggest waters; the typical Washington lake is far smaller.

Where to stay near Washington's largest lakes

Planning a trip? Jump to live cabin, resort, and hotel availability near Washington's biggest lakes.

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