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Lake Harriet Water Resources

Part of: Lake Harriet Park

Known for the landmark band shell on its shoreline, Lake Harriet is one of the largest lakes in the Chain of Lakes. With many ways to enjoy the lake including sailing, paddling, fishing and swimming, it is a favorite summer destination for visitors. The nearby rose and rock gardens, bird sanctuary, and historic streetcar are additional attractions for those who come for concerts and special events at the band shell each summer.  Lake Harriet has excellent rankings in all aspects of the Index with its beautiful aesthetics, available habitat, high water clarity, consistently low bacterial levels, and variety of ways for visitors to enjoy the lake.

Recent Secchi Disk Readings

August 7, 2019
Secchi Depth (feet): 4.9

About Secchi Disk Readings

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.

Recent Beach Status

Lake Harriet North Beach

8/19/2019
E Coli: 45
Water Temp: 64˚ F
Status: Open

Visit Lake Harriet North Beach

Lake Harriet Southeast Beach

8/19/2019
E Coli: 21
Water Temp: 63 ˚ F
Status: Open

Visit Lake Harriet Southeast Beach

What does the E. coli level mean?

Escherichia coli (E. coli) is a surrogate measure, or indicator for fecal contamination in recreational waters. Indicator organisms themselves do not cause illness under normal conditions. Elevated bacteria levels generally occur in aquatic environments after rain events when bacteria from various sources are washed into the lakes. Potential sources of E. coli in lake water include:

  • Foreshore beach sand
  • Organic debris
  • Leaking diapers, bather defecation
  • Polluted stormwater runoff
  • Sewage spills near the beach
  • Sewer line break discharges
  • Stream inflows
  • Wild and domestic animal waste

We test beaches weekly from June through August for E. coli bacteria, which can indicate a health risk. We follow Minnesota Pollution Control Agency guidelines for beach closures. Two types of results will close a beach:

  1. Single-Sample Limit: A single result of over 1,260 organisms per 100 mL of water
  2. Geometric Mean: Five samples equally spaced over a 30-day period exceed 126 organisms per 100 mL of water

Elevated bacteria levels in MPRB lakes usually occur as a result of rain events and return to normal levels within 24 to 48 hours of the rain event.

We will re-sample, and reopen the beach only when bacteria levels are within state guidelines.

We also provide water quality information on the beach status hotline: 612-313-7713

Beach Water Quality Factors

Each summer, thousands visit our City lakes and enjoy a refreshing swim at our many swimming beaches. To ensure a healthy and enjoyable experience for these swimmers, we monitor the water at the public beaches for E. coli, bacteria that can be an indication of health risks for swimmers.

Beaches close if a water sample does not meet the State of Minnesota’s guidelines. A beach reopens when testing reveals that levels are within guidelines. The test for E. coli takes 24 hours, and results are posted early afternoon the day after we sample a beach.  The closing of a Minneapolis beach is rare, and in most cases the beach will re-open quickly.

Bacteria Levels Rise with Rainfall

High bacteria levels generally occur immediately after rain events in Minneapolis. Here’s what you should be aware of regarding bacteria levels:

  • Pick up after your Pet: Increased bacteria levels predominantly come from waterfowl and pet wastes in yards, streets and parks that wash into lakes either directly or through the storm sewers as the result of a heavy rain.
  • Avoid Swimming after a Rainfall:  Elevated bacterial levels in lakes generally return to normal levels within 48 hours of a rainfall.
  • Swim Healthy:  Avoid swimming if you or your child have diarrhea, to prevent the transmission of the disease.
  • Keep it Clean:  Be careful to not get lake water in your mouth. Wash your hands before eating and after changing a diaper. Shower afterwards if possible.

Summer Heat Attracts Swimmer's Itch

Swimmer’s Itch occasionally affects our City lakes and beaches. Here’s what you should know about this annoying but harmless irritation:

  • To avoid becoming infected, towel dry immediately after exiting the water and shower afterwards, when possible.
  • Characterized by small, irritating red welts that appear after swimming. Sensitive individuals may itch for several weeks.
  • Occurs most often after swimming on hot, still summer days.
  • Caused by a parasite that infects birds and snails during different stages of its life. The parasite is unable to live in humans.

Lake Aesthetic and User Recreation Index (LAURI)

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)

The score for each lake is based on the geometric mean number of Escherichia coli (E. coli) collected by the beach monitoring program (Table 1-1).  Lakes with more than one beach were averaged together.  EPA and Minnesota guidelines state that beaches should not exceed a geometric mean of 126 organisms per 100 mL during a 30-day time period.  Lower numbers of organisms indicate less risk of illnesses for lake users.

Table 1-1.  Scoring for the public health portion of LAURI.

E. coli, (CFU/100mL)* Score
<2 (ND) 10
2-10 9
11-20 8
21-35 7
36-50 6
51-65 5
66-80 4
81-100 3
101-125 2
>126 1

 

 

 

 

 

 

 

 

 

 

 

 

* The value used is the running geometric mean for the year, averaged for all the beaches on a lake.

Water Quality Index (water clarity/Secchi depth)

Water clarity is a good integrator of various parameters affecting the quality of a lake. The average Secchi transparency reading from all the data collected during the growing season is used. The lakes are separated into deep lakes and shallow lakes using criteria developed by the Minnesota Pollution Control Agency (MPCA). A shallow lake is defined as 80% littoral (< 15 feet deep). Bde Maka Ska, Cedar, Harriet, and Wirth are considered deep lakes. Loring, Isles, Hiawatha, Nokomis, and Powderhorn are considered shallow lakes. Greater secchi depth indicates clearer water.  LAURI scoring is shown below in Table 1-2.

Table 1-2.  Scoring for the water quality portion of LAURI.

Secchi Depth (m) Deep Lake Score Shallow Lake Score
0-0.5 1 2
0.6-1 2 4
1.1-1.5 3 6
1.6-2.0 4 8
2.1-2.5 5 10
2.6-3.0 6
3.1-3.5 7
3.6-4.0 8
4.1-4.5 9
>4.6 10

Habitat Quality (aquatic plant and fish diversity)

LAURI assessments of habitat quality are based on detailed Minneapolis Park and Recreation Board (MPRB) surveys and DNR fish sampling. Scoring is based on presence of aquatic plants, density of plants, and amount of coverage (Table 1-3). Lakes with more aquatic plants receive higher habitat quality index scores.  Points are also awarded for more diverse fish populations. Each fish score is based on the most recent available DNR fish survey done for a lake. The score from the aquatic plant and fish surveys are averaged for the LAURI.

Table 1-3. Scoring for the habitat portion of LAURI.

Macrophyte
Species
Score Density Score Coverage
>15 ft.
Score # Fish
Species
Score
0 0 Low 0 0-25 2 <=6 2
1-4 3 Low-Med 3 25-50 4 7-8 4
4-8 6 Medium 6 50-75 7 9-11 6
8-15 8 Med-High 8 75-100 10 12-14 8
>15 10 High 10 >=15 10

Recreational Access (availability and ease of public access)

The lakes are also scored for the quantity and quality of recreational access to the water. The recreational score considers the number of fishing docks, beaches, boat launches, intra lake connections, boat rentals, canoe racks and sail boat buoys, boardwalks, picnic areas and concessions at a lake, Table 1-4. While aquatic plants are a necessary part of a healthy lake ecosystem they can also interfere with recreational uses of the lake.  Lakes also receive points for invasive plant growth management.

Table 1-4. Scoring for the recreational access portion of LAURI.

Recreational Opportunities # RecOps at Site Total # RecOps +
Aquatic Plant Mgmt
Final Score
Fishing Dock 0 1
Beach 1 2
Boat Launches 2 3
Intra Lake Connection 3 4
Boat Rental 4 5
Boat Storage 5 6
Boardwalk 6 7
Picnic Area 7-8 8
Concessions 8-9 9
Aquatic Mgmt = yes (+4) >10 10
Aquatic Mgmt = no (+0)
Total # RecOps at site +
Aquatic Plant Mgmt

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

The lakes are scored for water color, odor, and debris based on an assessment done from shore, dock, or boat, Table 1-5.  Higher numbers indicate better aesthetics.  The scores are averaged over the season.  Aesthetics can be difficult to evaluate because they are qualitative and dependent on individual experience.

Table 1-5.  Scoring for the aesthetic portion of LAURI.

Color Score Odor Score Debris Score
Clear 10 None/Natural 10 None 10
Lt. Brown or
Green
8 Musty-Faint 8 Natural 9
Bright Green 5 Musty-Strong 6 Foam 8
Milky White 4 Sewage/
Fishy/
Garbage-Faint
5 Piles of Milfoil
(>3)
7
Brown/
Reddish/
Purple
2 Sewage/
Fishy/
Garbage-Strong
2 Trash: Fixed
(>3)
4
Gray/Black 0 Anaerobic/Septic 0 Trash: Floating
(>3)
3
Many Dead Fish
(>5)
2
Green Scum 2
Oil Film 1
Sewage Solids 0

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