How’s Coal Creek Faring After the Marshall Fire? Take A Look Under its Banks.

The author looks up amid the rebloom along Coal Creek in Superior in June 2023.

The first time I visited Coal Creek was just after the Marshall Fire in January of 2022, and the scene was solemn. The melting white snow was speckled with black and rusty brown ash, and unrecognizable piles of charred building materials such as gnarled piles of burned insulation and twisted metal, were strewn along the banks. I watched as small but steady rivulets of snowmelt water flowed across burned buildings and vehicles, collected in gutters and then poured into the creek while combusted electronics, household chemicals, and scorched building materials rode along as flotsam. The smell of smoke and ash was pungent that day and for many months afterward, accompanied by a damp, sour, metallic note that simply could not be mistaken for a campfire. As I started to collect water samples to take back to the lab, I watched in disbelief as someone’s Christmas ornaments floated past me in the creek.

Wildfire is a natural and even healthy process, essential for many ecosystems to thrive. But the incineration of over 1,000 homes and buildings in the Coal Creek watershed was an undeniable human and environmental disaster. At the time, I had been using statistical methods to try to elucidate water contamination in data from the 2018 Camp Fire for my dissertation research at CU Boulder through a partnership with researchers in northern California. Suddenly, the Marshall Fire brought the reality of urban fire home. 

A week after the fire, with no funding secured but knowing the potentially dire impacts to the stream, my advisor Diane McKnight and I met one evening in her lab to start acid-washing bottles (an important step for water quality analysis). The next day we began collecting water samples to test for metals, nutrients, and other contaminants in the creek. Starting that February, we also began sampling creek bed organism populations to assess ecosystem health. (Learn more about our two years of monitoring Coal Creek on our StoryMap.)

Fast forward to present day 2024, an early February rain and snow event brought back memories of that day in January 2022. A few of the trees lining the creek still bear partial scorch marks, and during heavy rain, I sometimes think I can detect a hint of that damp, sour, ashy smell. Still, it’s hard to believe an urban firestorm raged through just two years ago. And yet though much of the visible damage has faded, lingering impacts on the watershed exist, invisible.

Beneath Coal Creek's rocky streambed lies the hyporheic zone, an underground region beneath and alongside the creek bed where water filters through gravel and sediment. In this subsurface zone, microscopic life flourishes, supporting the health of the entire watershed. The hyporheic zone also acts as a filter for contaminants and regulates essential stream processes. However, urbanization combined with the aftermath of the Marshall Fire now limit this sensitive habitat, putting the delicate balance of the creek ecosystem at risk. 

Two Worlds in One Watershed

If you want to know how healthy a stream is, look to its bioindicator insects. Stoneflies, mayflies, and caddisflies are generally sensitive organisms that generally require high water quality to thrive. On the other end of the spectrum, pollution-tolerant leeches and bloodworms (red chironomids) indicate poor stream health.

Upstream, Coal Creek at the Mayhoffer-Singletree Trail in the Superior Associates Open Space is defined by a healthy riparian vegetative border and limited urbanization. Experiments by our lab group show an extensive hyporheic zone in this channel. This stretch of creek maintains a sanctuary for sensitive aquatic life, particularly during dry periods when surface flows recede. Here, gravel and sediments act as a sponge, harboring moisture and providing refuge for benthic organisms such as mayflies and stoneflies - linchpins of the food web and sustenance for species including the northern leopard frog, burrowing owl and beaver.

Less than a mile downstream, a different story emerges. Near the underpass of US 36, a degraded section of Coal Creek sees the hyporheic zone constrained by both urban impacts and fire damage. Even before the fire, restoration efforts sought to improve the area through park creation and habitat projects. The urbanized streambed already suffered from channelization (e.g. concrete hardening and piping of the creek), separating the waterway from floodplain habitat and efficiently delivering pollution washed from roads and parking lots. 

The Marshall Fire has worsened these issues by introducing heavy metals that continue leaching into the creek during rains. Where sensitive species such as stoneflies were found in 2019, new pollutant burdens now jeopardize their survival. This is the stretch of the creek where burned urban debris settled after the fire. Much of that debris has since sunk into creek sediments where it may continue to release pulses of toxic contaminants during rains or snowmelt. It is now bloodworm country, indicating the stressors this urban stretch of Coal Creek faces.

Gauging the Creek’s Health

So what is Coal Creek’s overall post-fire health? Our assessments show that it varies. Degraded zones lag while more intact areas display hardiness when given the space to self-heal. Yet even resilient stretches like Superior Associates face hydrologic interruption and other challenges. Restoration of the heavily damaged urban corridors is likely needed to aid Coal Creek’s recovery and uphold this watershed for future generations to enjoy. 

I’ll never forget the smell of ash and snow, nor the sorrow of those who lost everything that day in December. Our research began by quantifying the visible impacts to Coal Creek through water and biological sampling. Over two years later, much of the surface damage has faded, but hidden disruptions linger. The opportunities exist to regenerate lost buffers, renew hyporheic zones, and boost the creek’s regenerative potential. This calls for united action across agencies, local groups, and communities who all have a stake in Coal Creek’s revival. Together, we can implement rehabilitation measures to steer this urban ecosystem back towards balance. The promising news? Coal Creek resiliency endures, ready to rebound given the resources and space to do so.