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

Updated August 2026

Biggest Lake in Iowa: Lake Red Rock (15,250 acres)

Lake Red Rock is Iowa's largest lake per the Iowa DNR (Fish Iowa lake database). Below: 50 Iowa lakes ranked by surface area.

The largest lake in Iowa is Lake Red Rock at 15,250 acres , in Marion County, according to the Iowa DNR (Fish Iowa lake database).

See our Lake Red Rock water-quality report card NR

Source: Iowa DNR (Fish Iowa lake database) (2026-07-30). The table below ranks the Iowa lakes in our own index by surface area.

Lakes with area data

11,013

Largest (acres)

443

Median of top 50

20/50

Reservoirs (vs natural)

Reading Iowa's size profile

Iowa's largest lake by surface area is Rathbun Lake in Appanoose County, spanning 11,013 acres. Most of Iowa'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 Iowa by surface area

#	Lake	County	Surface area	Max depth	Grade
1	Rathbun Lake	Appanoose	11,013 acres	-	C
2	Lake Red Rock	Marion	8,619 acres	-	NR
3	Saylorville Lake	Polk	5,428 acres	-	NR
4	Lake Odesa	Louisa	1,744 acres	-	NR
5	Lake Panorama	Guthrie	1,179 acres	-	NR
6	Trumbull Lake	Clay	1,061 acres	-	NR
7	Town Lake	Jackson	956 acres	-	NR
8	Lake Macbride	Johnson	950 acres	-	D
9	Rice Lake	Winnebago	891 acres	-	NR
10	Big Creek Lake	Polk	885 acres	-	F
11	Three Mile Lake	Union	880 acres	-	D
12	Little River Lake	Decatur	787 acres	-	F
13	Swan Lake	Emmet	766 acres	-	NR
14	Big Lake	Allamakee	704 acres	-	NR
15	Lake Icaria	Adams	700 acres	-	F
16	Brushy Creek Lake	Webster	690 acres	-	F
17	Lake of the Hills	Scott	657 acres	-	C
18	Rock Creek Max Depth Lake	Jasper	640 acres	-	F
19	Twelve Mile Lake	Union	633 acres	-	F
20	Lake Sugema	Van Buren	574 acres	-	F
21	High Lake	Emmet	555 acres	-	NR
22	Cedar Lake	Chickasaw	542 acres	-	NR
23	Hartwick Lake	Delaware	506 acres	-	NR
24	South Twin Lake	Calhoun	465 acres	-	NR
25	Rush Lake	Palo Alto	457 acres	-	NR
26	Upper Brown Lake	Jackson	443 acres	-	NR
27	Eagle Lake	Hancock	434 acres	-	NR
28	Pleasant Creek Lake	Linn	410 acres	-	D
29	Sun Valley Lake	Ringgold	398 acres	-	NR
30	Forneys Lake	Fremont	398 acres	-	NR
31	Big Wall Lake	Wright	384 acres	-	NR
32	Mud Hen Lake	Allamakee	383 acres	-	NR
33	Lost Grove Lake	Scott	350 acres	-	C
34	Smith Pool	Kossuth	345 acres	-	NR
35	Green Valley Lake	Union	336 acres	-	F
36	Elm Lake	Wright	336 acres	-	NR
37	Silver Lake	Worth	314 acres	-	NR
38	West Lake Osceola	Clarke	306 acres	-	D
39	Lake Darling Max Depth	Washington	304 acres	-	F
40	Roberts Creek Lake	Marion	296 acres	-	F
41	Center Lake	Dickinson	287 acres	-	F
42	Wood Duck Slough	Clayton	286 acres	-	NR
43	Mud Lake	Clay	283 acres	-	NR
44	Dan Green Slough	Clay	278 acres	-	NR
45	Badger Creek Max Depth Lake	Madison	276 acres	-	F
46	Rush Lake	Osceola	276 acres	-	NR
47	Lizard Lake	Pocahontas	274 acres	-	NR
48	Sabula Lakes	Jackson	260 acres	-	NR
49	Elk Lake	Clay	256 acres	-	NR
50	Lake Belva Deer	Keokuk	247 acres	-	F

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Frequently Asked Questions

What is the largest lake in Iowa?

Lake Red Rock, at 15,250 acres, in Marion County. Source: Iowa DNR (Fish Iowa lake database), 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 Iowa's largest lakes natural or reservoirs?

Of the top 50 Iowa lakes by area, 20 sit on a dammed river (reservoirs) and 30 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 Iowa lake in this ranking?

Across the top 50 Iowa lakes by surface area, the median is 443 acres (Upper Brown Lake). This list is biased toward the biggest waters; the typical Iowa lake is far smaller.

Where to stay near Iowa's largest lakes

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

Deepest lakes in Iowa →Cleanest lakes in Iowa →Largest lakes (all states) →All Iowa lakes →