Fern Lake Fire

Northern Water managed a study in 2013 to determine the impacts of the Fern Lake Fire on water quality in the upper Big Thompson River.

The Fern Lake Fire in Rocky Mountain National Park started on Oct. 9, 2012 and burned approximately 3,500 acres before it was officially declared out in June 2013. The fire occurred within the headwaters of the Big Thompson River in an area (Forest Canyon) that had not burned in more than 800 years. At approximately 8,000 to 11,000 feet, the elevation of the burn area was higher than many of the recent fires in Northern Colorado.

A Collaborative Effort
The Fern Lake Fire Water Quality Study was a collaborative effort with costs shared by Northern Water, the Town of Estes Park, the cities of Loveland, Fort Collins, Greeley, Boulder and the United States Geological Survey. The Big Thompson Watershed Forum’s long-term Cooperative Water Quality Monitoring Program provided pre-fire data that were used to compare pre- and post-fire conditions. 

Study Objective
The objective of this study was to assess the impacts on upper Big Thompson River water quality from snowmelt and rainfall runoff originating from the burn area. Much of the burn area is in steep terrain, but this steep area is located upstream of a large, flat meadow (Moraine Park). The ability of this meadow to help mitigate impacts on downstream water quality was assessed. Additionally, because of the burn area’s high elevation, information about water quality impacts gained from this study may be applicable to future wildfires that occur within the higher elevation watersheds of the West and East Slope portions of the Colorado-Big Thompson Project.
Sampling Locations, Frequency & Parameters
The water quality impacts associated with the Fern Lake Fire were assessed using data collected at the three monitoring stations shown on the map above and in the table below.

Station  Description  Latitude  Longitude
Big Thompson River near Cub Lake trailhead, upstream end of Moraine Park, RMNP  40.35645  -105.6177
(BTWF M-10)
Big Thompson River downstream end of Moraine Park, RMNP  40.3539  -105.5841
(BTWF M-20)
Big Thompson River upstream of Lake Estes, approx. 5.2 miles downstream of BT-MPD  40.3785  -105.5138

Fern Lake Fire burn scar in Forest Canyon (photo taken Aug 2014).

View larger map
Watersheds draining to Fern Lake Fire Study monitoring sites BT-MPU, BT-MPD and BT-LEU.

Rigorous USGS Standard Field Protocols

All samples were collected by the USGS using its rigorous standard field protocols. Eight routine monthly sampling events were conducted from April 2013 through November 2013. During spring runoff, there were four additional sampling events at BT-MPU and BT-MPD such that six weekly samples were collected. Finally, there was one sampling event in August at BT-MPU and BT-MPD associated with a summer rainstorm runoff event.

The monitoring parameters included field measurements of temperature, dissolved oxygen, pH and specific conductance, and laboratory analyses for major ions, total organic carbon, dissolved organic carbon, total suspended solids (TSS), total dissolved solids, turbidity, nutrients and metals.
A detailed discussion of the results is presented in the Fern Lake Water Quality Study Report.  All of the data collected and assessed for this study are available at: http://www.northernwater.org/DynData/WQDataMain.aspx.

Water quality data collected in 2013 downstream of the Fern Lake Fire burn scar indicate that runoff from the burn area resulted in some water quality changes in the Big Thompson River upstream and downstream of Moraine Park (at BT-MPU and BT-MPD, respectively). However, the measured impacts were generally short-lived and not significant enough to impact aquatic life and drinking water supplies or occurred in parameters (major ions) that typically would not result in impacts to aquatic life or drinking water supplies. At the monitoring site just upstream of Lake Estes (BT-LEU), the collected samples showed minimal water quality changes.
Comparison of Upstream & Downstream Ends of Moraine Park
During the snowmelt runoff, TSS was higher at the downstream end of Moraine Park, likely due to the mobilization of finer sediments that do not have a chance to settle within Moraine Park. During the summer precipitation events, TSS was higher at the upstream end of Moraine Park than at BT-MPD. Intense summer storm events likely mobilize coarser sediments from the areas upstream of BT-MPU that can settle within Moraine Park prior to reaching BT-MPD. The chemical quality at BT-MPU and BT-MPD during 2013 was very similar, except for parameters that are associated with the suspended solids.