#	County	Water Quality Score	Overall Score
1	Big Horn County, MT	86	42.9
2	Broadwater County, MT	86	54.5
3	Carter County, MT	86	72.6
4	Daniels County, MT	86	67.8
5	Deer Lodge County, MT	86	48.9
6	Fallon County, MT	86	72.4
7	Garfield County, MT	86	67.7
8	Glacier County, MT	86	52.6
9	Judith Basin County, MT	86	77.5
10	McCone County, MT	86	75.3
11	Meagher County, MT	86	65.5
12	Musselshell County, MT	86	59.7
13	Petroleum County, MT	86	80.1
14	Powder River County, MT	86	67.7
15	Powell County, MT	86	59.4
16	Roosevelt County, MT	86	46.5
17	Sanders County, MT	86	60.6
18	Sheridan County, MT	86	49.3
19	Silver Bow County, MT	86	36.4
20	Stillwater County, MT	86	58.8
21	Sweet Grass County, MT	86	64.6
22	Wheatland County, MT	86	63.2
23	Ravalli County, MT	56.9	58.4
24	Flathead County, MT	55	39.8
25	Cascade County, MT	54.3	33.5
26	Gallatin County, MT	54.3	44.2
27	Park County, MT	47.9	48.9
28	Yellowstone County, MT	42.1	32.6
29	Missoula County, MT	40.6	35.1
30	Phillips County, MT	36.7	62.3
31	Teton County, MT	33.5	62.9
32	Beaverhead County, MT	32.9	63
33	Valley County, MT	32.7	56.1
34	Lake County, MT	30.7	40.5
35	Madison County, MT	28.6	65.6
36	Toole County, MT	27.2	49.1
37	Hill County, MT	26.5	34.1
38	Carbon County, MT	26.3	64.8
39	Lewis and Clark County, MT	26.1	38.4
40	Mineral County, MT	24.1	54.1
41	Lincoln County, MT	22.9	57.7
42	Chouteau County, MT	21.1	65.7
43	Pondera County, MT	15.1	51.5
44	Custer County, MT	13.5	48
45	Dawson County, MT	13.2	47.7
46	Wibaux County, MT	9.4	63.2
47	Richland County, MT	8.6	52.7
48	Rosebud County, MT	5.5	60.2
49	Jefferson County, MT	3.7	58
50	Golden Valley County, MT	2.2	69.9
51	Liberty County, MT	2.2	57.1
52	Granite County, MT	1.9	57.4
53	Fergus County, MT	1.5	56.6
54	Blaine County, MT	0.9	54.1
55	Treasure County, MT	0.2	69.5

Data Source

Water Quality data from WaterByCounty. See full details at WaterByCounty. Data updated February 2026.