Cass County Lake Quality

Minnesota, 133 lakes, average grade B (Good)

Cass County has 133 graded lakes, enough that within-county variation matters as much as the county average. Some are deep glacial basins, others are shallow agricultural-watershed waters, and the grade distribution reflects that mix. With an average grade of B, Cass County sits comfortably above the Minnesota median.

A meaningful share of Cass's lakes break 50 feet of depth, which matters because deep lakes hold cooler water all summer and resist the resuspended-sediment problems that plague shallow basins. The county's best-graded lake is Deep Portage Lake (A).

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Quick Answers for Cass County

Cleanest lakes in Cass County →Cleanest lakes in Minnesota →Safest swimming lakes in Minnesota →

Planning a trip? Check special fishing regulations for Deep Portage Lake, whether the fish are safe to eat, and the best times to fish — or browse the full Minnesota regulations index.

DNR Reports (319)

Minnesota DNR LakeFinder resources for lakes in Cass County. Showing 12 most recent — browse all reports →

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Fisheries Lake Survey — Widow
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Welch
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Webb
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Washburn
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Wabedo
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Vermillion
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Variety
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Upper Trelipe
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Upper Sucker
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Upper Gull
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Trillium
Fisheries Lake Survey · MN DNR LakeFinder
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Fisheries Lake Survey — Town Line
Fisheries Lake Survey · MN DNR LakeFinder

All Lakes in Cass County

Rank	Lake	Grade	Clarity	Max Depth	Phosphorus
1	Deep Portage Lake	A	15.4 ft	105 ft	10 µg/L
2	Horseshoe Lake	A	21 ft	51 ft	-
3	Long Lake	A	21.8 ft	115 ft	9 µg/L
4	Long Lake	A	16.8 ft	37 ft	-
5	Sand Lake	A	21 ft	54 ft	-
6	Girl Lake	A	17 ft	81 ft	12 µg/L
7	Bass Lake	A	-	55 ft	9 µg/L
8	Island Lake	A	15 ft	45 ft	12 µg/L
9	Island Lake	A	17.5 ft	40 ft	8 µg/L
10	Portage Lake	A	22.8 ft	84 ft	-
11	Hand Lake	A	17 ft	57 ft	-
12	Ox Yoke Lake	A	17.5 ft	42 ft	-
13	Crystal Lake	A	16 ft	40 ft	7 µg/L
14	Pleasant Lake	A	15.4 ft	72 ft	10 µg/L
15	Webb Lake	A	17.8 ft	84 ft	9 µg/L
16	Howard Lake	A	16 ft	60 ft	9 µg/L
17	Thunder Lake	A	16.4 ft	95 ft	10 µg/L
18	Sanburn Lake	A	19 ft	48 ft	-
19	Little Portage Lake	A	16.4 ft	-	11 µg/L
20	Pine Lake	A	16 ft	25 ft	13 µg/L
21	Ten Mile Lake	A	20 ft	208 ft	8 µg/L
22	Ponto Lake	A	19 ft	60 ft	7 µg/L
23	Sylvan Lake	A	19.8 ft	-	7 µg/L
24	Hunter Lake	A	31 ft	48 ft	11 µg/L
25	Lost Lake	A	15 ft	26 ft	8 µg/L
26	Stony Lake	A	23.3 ft	50 ft	7 µg/L
27	Widow Lake	A	18.5 ft	46 ft	-
28	Barnum Lake	A	16.1 ft	30 ft	9 µg/L
29	Mule Lake	A	18.7 ft	47 ft	9 µg/L
30	Little Webb Lake	A	16.5 ft	37 ft	-
31	Fawn Lake	A	20 ft	29 ft	-
32	Pillager Lake	A	15.1 ft	39 ft	7 µg/L
33	Cooper Lake	A	17.1 ft	70 ft	13 µg/L
34	Thunder Lake	A	20 ft	95 ft	-
35	Grave Lake	A	17.2 ft	55 ft	-
36	Mckeown Lake	A	16.5 ft	37 ft	10 µg/L
37	Kid Lake	A	15.5 ft	52 ft	11 µg/L
38	Long Lake	A	46.6 ft	115 ft	-
39	Walker Bay Lake	A	16.5 ft	-	-
40	Agency Bay Lake	A	15.2 ft	-	-
41	Kabekona Bay Lake	A	17.2 ft	150 ft	-
42	Jack Lake	A	15.7 ft	110 ft	7 µg/L
43	Pine Mountain Lake	A	17.5 ft	80 ft	-
44	Big Deep Lake	A	17.1 ft	107 ft	6.5 µg/L
45	11-0086-00 Lake	A	18.5 ft	55 ft	-
46	Craig Lake	A	-	-	-
47	Gijik Lake	A	-	-	-
48	Crooked Lake	A	12 ft	74 ft	12 µg/L
49	Steamboat Lake	A	12 ft	93 ft	11 µg/L
50	Boxell Lake	A	14.5 ft	27 ft	14 µg/L
51	Birch Lake	A	13.7 ft	45 ft	12 µg/L
52	Ada Lake	A	14 ft	60 ft	10 µg/L
53	Washburn Lake	A	14 ft	111 ft	11 µg/L
54	Maple Lake	A	13.5 ft	45 ft	-
55	Woman Lake	A	14.1 ft	-	11 µg/L
56	Upper Gull Lake	A	10 ft	54 ft	19 µg/L
57	Rainy Lake	A	13.9 ft	29 ft	11.5 µg/L
58	Spider Lake	A	10.2 ft	17 ft	12.5 µg/L
59	Gull Lake	A	14.5 ft	80 ft	14 µg/L
60	Upper Trelipe Lake	A	14 ft	69 ft	11 µg/L
61	Ray Lake	A	10 ft	27 ft	11 µg/L
62	Lawrence Lake	A	10 ft	71 ft	16 µg/L
63	Child Lake	A	11.3 ft	29 ft	14 µg/L
64	Baby Lake	A	12.5 ft	69 ft	9 µg/L
65	Inguadona Lake	A	12.1 ft	79 ft	15 µg/L
66	Roosevelt Lake	A	11 ft	129 ft	12 µg/L
67	Broadwater Bay Lake	A	14.5 ft	54 ft	14 µg/L
68	Blackwater Lake	A	14.1 ft	67 ft	11 µg/L
69	Man Lake	A	11.2 ft	93 ft	9.5 µg/L
70	Little Boy Lake	A	11 ft	74 ft	14 µg/L
71	Wabedo Lake	A	10 ft	95 ft	16 µg/L
72	Trillium Lake	A	11.2 ft	48 ft	17 µg/L
73	Loon Lake	A	12.1 ft	25 ft	13 µg/L
74	Sugar Lake	A	12 ft	44 ft	17 µg/L
75	Pine Mountain Lake	A	12.5 ft	80 ft	17.5 µg/L
76	Hay Lake	A	13.2 ft	56 ft	16.5 µg/L
77	Portage Bay Lake	A	11.3 ft	-	-
78	Traders Bay Lake	A	10 ft	-	-
79	Welsh Lake	A	13.5 ft	59 ft	-
80	Welch Lake	A	12.5 ft	59 ft	11 µg/L
81	Five Point Lake	A	12.8 ft	37 ft	16 µg/L
82	Lake Winnibigoshish	A	16 ft	69.8 ft	-
83	Tamarack Bay Lake	A	11.5 ft	69.8 ft	-
84	Horseshoe Lake	B	8.9 ft	12 ft	18 µg/L
85	Leech Lake	B	12.5 ft	-	11.5 µg/L
86	Silver Lake	B	13 ft	20 ft	14 µg/L
87	Swift Lake	B	7.5 ft	52 ft	13.5 µg/L
88	Steamboat Bay Lake	B	9.8 ft	150 ft	14 µg/L
89	Upper Sucker Lake	B	10.8 ft	25 ft	17 µg/L
90	Six Mile Lake	B	11.5 ft	68 ft	16 µg/L
91	Portage Lake	B	12 ft	65 ft	-
92	Kidney Lake	B	11.5 ft	55 ft	-
93	Three Island Lake	B	9 ft	13 ft	12 µg/L
94	Andrus Lake	B	12 ft	55 ft	-
95	Little Andrus Lake	B	13 ft	37 ft	-
96	Hattie Lake	B	9.8 ft	30 ft	17 µg/L
97	Variety Lake	B	10.5 ft	29 ft	-
98	Leavitt Lake	B	8.4 ft	60 ft	19 µg/L
99	L Thunder Lake	B	14 ft	-	-
100	Blackwater Lake	B	13.1 ft	67 ft	-
101	Inguadona Lake	B	12.5 ft	79 ft	-
102	Boy Bay Lake	B	7.4 ft	-	-
103	Shingobee Bay Lake	B	10.6 ft	-	-
104	Headquarters Bay Lake	B	7.5 ft	-	-
105	Sucker Bay Lake	B	8.8 ft	-	-
106	Town Line Lake	B	6.6 ft	11 ft	11 µg/L
107	3-Island Lake	B	9.8 ft	13 ft	-
108	Stevens Lake	B	10.2 ft	63 ft	28.5 µg/L
109	Portage Lake	B	7.5 ft	55 ft	23 µg/L
110	Lower Sucker Lake	B	8.3 ft	35 ft	22 µg/L
111	Island Lake	B	8.2 ft	-	20 µg/L
112	Portage Lake	B	7 ft	-	21 µg/L
113	Lower Trelipe Lake	B	6.9 ft	32 ft	23 µg/L
114	Little Sand Lake	B	7.5 ft	12 ft	24 µg/L
115	Boy Lake	B	8.9 ft	45 ft	21 µg/L
116	Big Portage (E Bay Lake	B	7.9 ft	23 ft	20 µg/L
117	Dade Lake	B	5.2 ft	-	12.5 µg/L
118	Big Portage (W Bay Lake	B	7.5 ft	23 ft	20 µg/L
119	Gould Lake	B	5 ft	-	-
120	Bowen Lake	B	13.7 ft	25 ft	32 µg/L
121	Little Wolf Lake	B	9.3 ft	24 ft	25 µg/L
122	Vermillion Lake	B	7.1 ft	27 ft	26 µg/L
123	Norway Lake	C	6.6 ft	12 ft	20.5 µg/L
124	Leech Lake	C	9 ft	-	-
125	Rock Lake	C	5.9 ft	17 ft	29.5 µg/L
126	Faherty Lake	C	6.2 ft	-	26.5 µg/L
127	Million Lake	C	5 ft	20 ft	21 µg/L
128	Margaret Lake	C	5.5 ft	26 ft	41 µg/L
129	George Lake	C	4.5 ft	20 ft	40 µg/L
130	Middle Sucker Lake	C	4.8 ft	20 ft	32 µg/L
131	Middle Sucker Lake	C	4.8 ft	-	-
132	Bueber Lake	C	6.2 ft	32 ft	37 µg/L
133	Abel Lake	D	5.7 ft	-	-

Source: EPA National Aquatic Resource Surveys, 2026.