4.5. SR 10-20-2003Item 4.5.
City
TO:
FROM:
DATE:
SUBJECT:
MEMORANDUM
Mayor and City Council
Stephen Rohlf, Building and Environmental Administrator
October 20, 2003 ~
Consider Curlyleaf Pond Weed Remediation in Lake Orono
Curlyleaf Pond Weed, a non native invasive aquatic plant, was first discovered in Lake
Orono last year. A survey of the lake this year revealed an alarming increase of this plant.
Left unchecked, this weed will totally clog shallow areas of waterways, which in Lake Orono,
is most of the lake. Potential remediafion measures for this problem include mechanical
harvesting, herbicide and freezing the plant out.
Members of the Lake Orono Improvement Association and city staff met with
representatives from the Minnesota Department of Natural Resources (DNR) Division of
Waters, Fisheries and Aquatic Plants on October 8, 2003 regarding what to do about
Curlyleaf Pond Weed in the lake. Staff is recommending the city do this third option (freeze
it out).
What is involved is a gradual four foot draw down of the lake (approximately over a one
week period), allowing the lake sediment to dry (approximately one week depending on
weather) and having cold enough temperatures to freeze the plant bulbs that are contained in
the sediment of the lake (approximately ten days). Drawing the lake down four feet will
eradicate the majority of the Curlyleaf Pond Weed, if temperatures are cold enough, while
still retaining enough water depth to avoid a fish kill. DNR Fisheries will determine when
the lake has to be refilled, even if weather conditions are not favorable for success. The
concern is having lake level back up before it gets too cold and oxygen starts to deplete in
the water.
Staff still needs to talk to the Elk River Municipal Utilities regarding the project. A potential
issue is having the gates for the dam freeze open, making it impossible to refill the lake, prior
to spring thaw. Staff will have an answer to this question for Monday night's meeting. Staff
will also have more certain dates for when a draw down of the lake would take place, but it is
most likely that it will occur in mid November. The cost for this remediafion is $0.
221st AVE
CO RD 21
33.
EV 03-06
P 03-13
co AS 03-04
I EV 03-05
Raver
CU 03-30
p 03-08
ZC 03-06
P 03-11
CU 03-27
V 03-03
175th AVE
CU 03-28
CU 03-26
65th AVE
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PROJECT LOCATIONS
OCTOBER 20, 2003
CITY COUNCIL
SHEEr