Lake Minnetonka water quality is monitored by the Minnehaha Creek Watershed District.  The MCWD has ten years of history on the water quality of Lake Minnetonka  as seen below for 20+ bays and lakes within the lake.

The Minnehaha Creek Watershed District grades Lake Minnetonka water quality as follows:
Grade A:  Beautiful, crystal clear water. Exceptional lakes that people can use recreationally without any issues.
Grade B:  Good water quality.  As the end of summer nears, algae may limit swimming.
Grade C:  Average water quality.  Relatively early in the season fishing, boating and swimming may be undesirable.  Algae may bloom occasionally.
Grade D:  Recreation on these lakes may be limited.  Severe algae problem may occur.
Grade F:  Recreational us can be severely limited.  Water tends not to be enjoyable.

Lake Minnetonka Subwatershed

* Bays not monitored due to water quality similar to adjacent bay
– Water body not monitored in 2017
n/a insufficient data