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.
THE WAKE-UP CALL
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?
LOVING IT TOO MUCH
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.
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”.
WORKING TO GET A-TURN-AROUND
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
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
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
WORKING TO GET BACK TO CLEAR
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
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.
LET’S KEEP GOING!
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”.