Odor Update: Southeast Fort Collins

strong odor in southeast Fort Collins. Update: Southeast Fort Collins
Odor Update: Southeast Fort Collins

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Strong odor in southeast Fort Collins


By Mark Sears,

Natural Areas Manager,

msears@fcgov.com, 970-416-2096



The City of Fort Collins Natural Areas Department (NAD) has received many complaints over the last week of a very strong odor in southeast Fort Collins. On Monday, 7/8 we determined that the odor is in part, if not largely coming from Duck Lake, which is managed by NAD as a part of the Fossil Creek Reservoir Natural Area. Duck Lake is on the south side of Carpenter Road, east of Timberline Road.

The City of Fort Collins and Larimer County are very sorry about the discomfort the odor from Duck Lake has caused many in the surrounding area.

City of Fort Collins Water Quality staff tested the water in Duck Lake and determined that the oxygen level is extremely low, which caused the algae to die and start decomposing, which causes the hydrogen sulfide odor. Other shallow bodies of water in the area are likely experiencing the same lack of oxygen and may be contributing to the problem. The situation at Duck Lake is extremely complex and not an easy problem to fix quickly.

Here is a list of actions NAD is taking or has taken:

  • The City of Fort Collins Water Quality Lab has run water tests to help better understand the issues and identify potential solutions.
  • Seeking advice from an aquatic consultant who has historically helped the Parks Department solve similar issues. Some  direction has been provided and a follow-up meeting scheduled  next Monday based upon the availability of the consultant.
  • At the request of the consultant, we have completed a bathometric survey of the lake to determine the surface area and volume; which are needed to calculate amounts of chemicals that could potentially be used to mitigate the odor and reduce the algae.
  • Met with two adjoining landowners/farmers to explore options for using NAD-owned irrigation water to fill and possibly flush water out of Duck Lake. Adding water may help aerate the water and flushing the lake could help even more; we are awaiting a final opinion from water quality experts. We have found one good option to run water and are working on another.
  • Renting 1000’ of pipe that will be installed on 7/12 to direct NAD irrigation water into Duck Lake, perhaps starting within the next 4-5 days.
  • Working to rent additional water to potentially enable flushing Duck Lake and possibly Mud Lake.
  • Reactivated one of the two Solar Bees, which are floating pumps designed to improve oxygenation in the lake to help prevent or reduce odors, that had shut down over a year ago when the lake became too shallow for them to operate. The intent is to  have the second Solar Bee replaced by the end of next week. The company that maintains them comes from Montana.  They are going to assess our situation to determine if more Solar Bees would be beneficial; if determined to be beneficial it will be approximately 8 weeks before they can manufacture and install the additional Solar Bees.
  • Meeting with representatives from Bio Char Now on 7/12. This Berthoud Company produces charcoal from pine beetle kill lumber and wood waste from the Larimer County Landfill. They claim that their Bio Char Now filters can remove the nutrients from the water which are causing the odor as well as absorb the hydrogen sulfide odor.
  • Also exploring several other potential short-term and long-term solutions.

We are working hard to do what we can now in the short term to mitigate the odor, and we are very sorry about the discomfort this odor has caused so many citizens. Unfortunately, there may not be much we can do other than let nature run its course and work to prevent the problem in the future.

Duck Lake and the upstream Mud Lake was jointly purchased in 2001 by Larimer County Open Lands and the NAD to be managed as a part of the Fossil Creek Reservoir Regional Open Space (now Natural Area). The first major episode of odor occurred in 2002. Larimer County which managed Duck Lake from 2001 to 2011 commissioned three studies over the next two years to assess the situation and evaluate potential solutions.

The situation is that Duck and Mud Lakes are natural very shallow (less than 5’ deep) lakes. They receive a very heavy nutrient load from surrounding agriculture fields, a dairy and from the waterfowl that frequent the lakes. The lakes are filled by rainfall runoff from the small surrounding agricultural drainage basin which absorbs most of the rainfall, small amounts of irrigation water that drains from adjoining fields, and from ground water. These sources contribute to the nutrient loading without providing much water to flush the lake. The nutrients cause the algae to bloom and use up the oxygen in the lake, the lake goes eutrophic. The dying algae decomposes producing hydrogen sulfide, methane, and ammonia gases which caused the odors and very poor water quality. Both Duck and Mud Lake are highly eutrophic and had been for many decades prior to the City and County purchasing them. The 2002 study stated that “the process going on at Duck and Mud Lake is a natural process that occurs in many closed basin systems, which goes through times of drying and concentration of chemical elements.”

The consultants hired in 2002 – 2004 recommended the following actions would improve the water quality:

  • Remove the nutrient loading coming from the surrounding agriculture.
  • Remove the nutrient loading from the sediment in the lake by removing the three plus feet of sediment from under the lake.
  • Increase the flow of water through the lake.
  • Improve the aeration of the water in the lake.

The only action Larimer County was able to take was the installation of two Solar Bees (water pumps)  in 2006 to improve the aeration of the water.

NAD took over the management of the lakes in about 2011, about the time another odor episode occurred. NAD hired a consultant to prepare a plan to control the odor and monitor the progress. While the plan implemented over two years was not successful it helped to better understand the significance and complexity of the problem.

Now in 2019 the conditions have created another major odor problem; many residents that have lived in the area for a long-time state that this is the worst odor problem in over 20 years. Unfortunately, the Solar Bees had stopped working due to the shallowness of the lake. The heavy rains this spring filled the lake making it possible to reactivate the Solar Bees. It is possible that the odors may have been reduced if the Solar Bees had been activated a few weeks earlier once the lake reached enough depth. The company that maintains the Solar Bees comes from Montana and were not scheduled to come to Fort Collins until later.

City of Fort Collins is working hard to do what we can now in the short term to mitigate the odor, and we are very sorry about the discomfort this odor has caused so many residents. Unfortunately, there may not be much we can do other than let nature run its course and work to prevent the problem in the future.