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  • HDT Team

Serpent Lake's Fight to be Clear Again

This article was written by Arlen Bowen and authorized by the Serpent Lake Association on June

24, 2020. Serpent Lake is an example of strong leadership and cooperation to turn around a

lake in trouble. It is reprinted here with permission.


A wake-up-call for many living on or near Serpent Lake came on

September 29, 2003. An algae bloom covered 80% of the lake’s north shoreline

for the next 5 days. Old-timers report that it was the first-time they saw such a

large bloom. Algae increased to the point where dead algae piled up on the

surface up to 70 feet from shore. This was Serpent Lake’s “red tide”, thought

only to happen in warmer water with serious agricultural runoff. Was Serpent

Lake loved to death? Could that be the underlying cause for the algae bloom?


Serpent Lake sits at the top of a watershed; no cities upstream adding

contaminants and no large farm fields upstream adding runoff. In 1960, the Girl

Scouts counted only 127 docks on Serpent; the lake shore was not crowded.

In the 1977-1979 time frame the clarity of the lake was first measured by

the Serpent Lake Association (SLA) using a Secchi disk. This disk would

disappear when lowered 20.2 feet out in the middle of the lake in 50 feet of

water. The lake was crystal clear; the lake was number one for walleye fishing

for several years; there were jobs available in the area and best of all there

were lake lots available to build year-round homes.

People loved The Serpent.

Serpent is not a typical MN lake with just one town. Serpent has two

towns with storm sewer pipes running into the lake from everywhere. Cabins

and homes ended up being packed along nine miles of shoreline. By 2005, there

were 292 docks. Cabins became lake homes with 2 car garages, paved

driveways, no rain gardens and lawns mowed right down to the lake.

Crow Wing Soil and Water Conservation District reported that shoreline

development had increased to the point where Serpent Lake had a higher

impervious surface percentage within 500 feet of shore than 52 other lakes in

the county. Sixty lakes were in the study.

You can tell a lot about a lake's health by using a Secchi disk reading.

More impervious surface means more runoff, more runoff means more

phosphorus, more phosphorus means more algae, more algae means a lower

Secchi disk reading. The 20.2 foot average Secchi of the 1970's decreased year-

by-year until it reached its lowest average ever in 2012 of 12.1 feet.

The Serpent was “loved-to-death”.


Prior to the algae blooms of 2003 and 2004, people recognized the lake

needed help. The City of Deerwood stopped using a small upstream lake,

Cranberry, as a full-time lagoon in the 1970’s. Crow Wing County townships

adopted the 1989 MN Shoreland Standard which limited impervious surface

percentage on shoreline property.

In 2004, SLA started a robust water testing program with standards

supported by MPCA and data admissible in a court of law. Variations in the

annual Secchi value were reduced by averaging 12 evenly-spaced readings

between June 1 and September 30.

Lakeshore owners spoke out strongly in 2005 to reject a zoning change for

the development of a high-density housing complex with a large marina out into

the lake

An overhead view of Serpent Lake indicating clarity along the shore.

Aerial photographs by AW Research identified properties with extra

heavy algae growth by their shore. SLA paid to have the photos taken and then

supported the testing of all 143 septic systems not tested in the last 5 years.

Lakeshore owners, without being asked, replaced the 30 cesspools found with

holding tanks or drain fields. Phosphorus seepage into the lake was reduced.

In 2005, The state required shoreline fertilizer must be phosphorus-free.

SLA delivered a free bag of it to every lakeshore owner to help sell the idea.

The City of Crosby and SLA funding helped divert runoff from Cross Ave

into two rain gardens in 2009. Many SLA members adopted buffer zones along

their shore to reduce lawn clippings, leaves, and runoff from entering the lake.

Plants in the buffer zone have very long root systems that absorb runoff and

capture phosphorus.

All this effort, over 30 years, combined to slow the year-to-year decline in

clarity to one foot every 5.7 years. A big push is needed to get headed back to

clearer water.


In 2012, a two-year study ended that looked at many sources of

phosphorus. A partnership started, supported and funded by SLA, Crow Wing

Soil and Water Conservation District (CW SWCD) and MPCA to collect data. This

data was used in the watershed model to quantify individual phosphorus

sources. SLA contributed by recording stream flows in and out of the lake and

their phosphorus levels. The final report identified the top three contaminant

sources as runoff from Crosby, runoff from Deerwood and stream flow from

Cranberry Lake.

SLA was named the 2013 “The Crow Wing County’s Conservationist of the

Year” award by CW SWCD.

In 2014, using the 2012 study results, a $1.2 million Legacy Fund grant was

awarded by BWSR/MPCA to reduce annual phosphorus in Serpent by 78 pounds

(20 percent) or the equivalent of 20 tons of algae. The grant had four goals:

reduce Crosby storm water runoff, reduce Deerwood storm water runoff, reduce

phosphorous levels in Cranberry Lake and upgrade zoning ordinances to reduce

storm water runoff around the entire shoreline.

In 2016 to 2018, Legacy Funds were spent diverting Crosby and Deerwood

runoff into holding ponds and filtration systems. Cranberry Lake’s total

phosphorus concentration was reduced 75% by treating it with alum. Three of

four governmental units on Serpent Lake adopted new storm water runoff


The 2017 clarity was 18.3 feet, an increase in clarity of over 6 feet in just 5

years. Secchi readings, after 2017, had some “degradation” from bike path

construction and some “improvement” due to Zebra Mussel filtering out algae.

Flow out of Serpent Lake each year is only 33% of the lake’s total volume.

This percentage means projects completed in 2018 will contribute to clarity

improvements in 2019, 2020 and 2021.


In 2019, Serpent Lake Secchi disk readings averaged 21.7 feet. The best

ever recorded. Better than the “bench-mark” years of 1977- 79, when the

three-year average was 20.2 feet.

The City of Crosby received the 2019 “Minnesota Community

Conservationist Award” for reducing city runoff into Serpent from 14 acres

along SE Second Street.

Serpent needed many projects, over 40+ years, to show a lake’s decline

can be reversed and returned to its former crystal-clear state. Serpent Lake is

one of the first in MN to demonstrate that a serious decline can be reversed.

There is now hope for other lakes dealing with serious algae bloom.

Serpent Lake has had an unexpected consequence by reducing

phosphorus and algae mass for water clarity. The Zebra Mussel hatch in May of

2019 had a death rate of over 99%. The yearlings died from the lack of algae as

they grew. This low survival rate was predicted by a large lake study in Ontario

Canada where clearer lakes had fewer Zebra Mussels.

An unexpected blessing… The Serpent is BACK-TO-CLEAR.

Thanks to SLA members, many government officials, CW SWCD, BWSR

and finally, the taxpayer’s support of the Legacy Fund.


The Ontario study also shows that with a clarity increase of another two

or three feet, Serpent would have NO Zebra Mussels. This is within reach.

Consider reducing runoff by building a rain garden or adding a “No-Mow” buffer

zone along the shore or using pavers to add (or replace) a driveway or patio.

Remember to use only phosphorus-free lawn fertilizer.

Let’s keep going and get both: no Zebra Mussels and great clarity. That

would be “VERY unexpected”.


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