Oligotrophic Lakes in Colorado

18 oligotrophic lakes in Colorado. Low nutrients, clear water, excellent for swimming.

An oligotrophic lake is what most people picture when they think of pristine northern lake country: clarity to depth, no algal scum, cold water that holds dissolved oxygen all the way to the bottom even in August. Across {{stateName}}, 18 lakes register as oligotrophic — 0% of them break 50 feet of depth, which is the structural condition that underwrites the trophic class. Without depth and a low-nutrient watershed, oligotrophy is hard to sustain.

On the LakeGrade rubric, oligotrophic lakes almost always pull an A or B — the same low-nutrient conditions that produce the trophic class also produce the high grade.

#	Lake	County	Grade	Clarity	Depth	TSI
1	Standley Lake	Jefferson	A	20.5 ft	-	34
2	Lake Nighthorse	La Plata	A	18.7 ft	-	35
3	Island Lake	Delta	A	16.7 ft	-	37
4	Rampart Reservoir	El Paso	A	28.5 ft	-	29
5	Turquoise Reservoir	Lake	A	16.1 ft	-	37
6	Little Eldorado Lake	San Juan	A	-	-	24
7	Upper Sunlight Lake	La Plata	A	-	-	27
8	Upper Grizzly Lake	La Plata	A	-	-	37
9	Seven Lakes	Jackson	A	-	-	38
10	White Dome Lake	San Juan	A	-	-	27
11	Arkansas Lake	Prowers	A	-	-	37
12	N St Vrain Lake	Boulder	A	-	-	38
13	Pearl Lake	Routt	B	14.1 ft	-	39
14	Mountain Home Reservoir	Costilla	B	14.4 ft	-	39
15	Antero Reservoir	Park	B	14.8 ft	-	38
16	Haviland Lake	La Plata	B	13.8 ft	-	39
17	Twin Lakes East	Lake	B	14.1 ft	-	39
18	Lake John	Jackson	B	13.8 ft	-	39

All oligotrophic lakes →Minnesota version →Wisconsin version →Illinois version →Michigan version →Iowa version →Ohio version →Pennsylvania version →New York version →Missouri version →Indiana version →North Dakota version →South Dakota version →Florida version →North Carolina version →All Colorado lakes →

Source: EPA National Aquatic Resource Surveys, 2026.