Powderhorn Lake is a 12-acre lake in one of the largest parks in the Minneapolis system. Many water quality restoration projects have occurred at Powderhorn since its original purchase in 1890 including: dredging, aeration, groundwater augmentation, shoreline restoration, stormwater best management practices, alum and barley straw treatments. The Minnesota Department of Natural Resources (MnDNR) has stocked the lake with fish as part of the Kid's Fishing Pond since 1980. Aquatic plants were first noted in surveys in 2006. The presence of aquatic vegetation represents an improvement in water clarity for a lake where the algae growth limited light penetration to the extent that little or no aquatic plants growth had occurred in the past. Powderhorn does not have a swimming beach and was therefore not scored for public health.

Water Clarity

Recent Secchi Disk Readings

October 17, 2018

Secchi Depth (feet): 1.9


About Secchi Disk Readings

secchi diagram

To measure water transparency with a Secchi disk, the disk is lowered from the shaded side of a boat until it cannot be seen. The depth of the water is recorded at the point where the disk reappears upon raising it from its original depth beyond visibility. It is important to remember that the Secchi measurement is a simple, approximate measurement of water clarity and can be influenced by various factors such as time of day, reader's eyesight, water color and suspended particles in the water. Therefore, Secchi disk readings should be used as a comparative tool to determine trends between lakes and over time.

  • Increased water clarity may be due to reduced nutrient inputs, seasonal algal cycles, decreased sediment inputs, and zooplankton grazing on algae.
  • Decreased water clarity may be due to large algal blooms, increased soil erosion inputs, wind circulation of sediments and nutrients, stormwater inputs, or a decrease in zooplankton.

Secchi readings for the lakes are done during the regular lake sampling schedule, with some lakes sampled every other year.


Lake Aesthetic and User Recreation Index (LAURI)

lauri graph for lake calhoun

The Lake Aesthetic and User Recreation Index (LAURI) was designed to give recreational users a source of information about conditions affecting their use of city lakes.  The goal is to have an accurate, science based and easily understandable recreational indicator for the public.  The  LAURI has five indices:

Public Health Index (E. coli measured at public swimming beaches)

Water Quality Index (water clarity/Secchi depth)

Habitat Quality (aquatic plant and fish diversity)

Recreational Access (availability and ease of public access)

Aesthetic Considerations (color and odor of water, garbage and debris)