A River of Chocolate Milk
Providing safe, clean drinking water when the Poudre River fills with sediment carried by runoff from snowmelt.
Sediment, ash, and debris from the 2020 Cameron Peak Fire fills the Cache la Poudre River in Larimer County, Colorado, during spring snowmelt and runoff between May 6 – 14, 2022. Video by Evan Barrientos/Platte Basin Timelapse.
In 2020, the Cameron Peak Fire burned more than 200,000 acres in the Cache la Poudre and Big Thompson watersheds. Almost two years later, we continue to see water quality impacts in the Poudre River, especially during spring runoff from snowmelt.
In the arid West, we’d expect to see impacts to river water quality following a wildfire during the summer monsoon season when high-intensity rainstorms occur over burned areas. These events can cause erosion of burned hillslopes, where sediment, ash, and other debris flow into surface waters, including streams, lakes, reservoirs, and eventually the Poudre River.
It was hard to miss the impact to water quality in the Poudre River last summer during monsoon season. Several post-fire storms turned the Poudre’s normally crystal-clear water black. The “black water” events lasted anywhere from a few hours to several days. Eventually, as water levels decreased, the sediment and ash settled and accumulated on the bottom and banks of the Poudre River and the clarity of the Poudre River improved.
Sediment from the 2020 Cameron Peak Fire accumulates in the Cache la Poudre Riverbed from July 27 – November 17, 2021. Video by Evan Barrientos/Platte Basin Timelapse.
This spring, as snow melts and runoff increases, we’re seeing the continued effects of the 2021 post-fire storm events. Over the past several weeks, water levels have risen and the Poudre River, at times, looks like chocolate milk.
It is not unusual for the clarity of the Poudre River to change with snowmelt runoff. The color of the water normally turns light brown, like tea; however, the changes this spring have been much more drastic due to the continued impacts from the Cameron Peak Fire. The extreme amount of sediment and ash stored on the bottom and banks of the Poudre River in 2021 is now being resuspended in the water as the river rises and its flow intensifies.
The Cache la Poudre River before (left) and during (right) runoff. Photos: Evan Barrientos/Fireforest/Platte Basin Timelapse
We anticipate the Poudre River will continue to look like chocolate milk until the sediment supply is limited or the flow of water is no longer strong enough to suspend and transport the sediment and ash downstream.
Turbidity (how murky water is) and river flows spiking during snowmelt in May 2022. Animation by Katie Willie/Open Eco Data Lab
Fort Collins Utilities is one of several water districts in Fort Collins that relies on water from the Poudre River to provide drinking water to residents, businesses, and industries in Northern Colorado.
Utilities is committed to providing high-quality, reliable drinking water to its customers year-round. Despite the challenging water quality conditions in the Poudre River so far this spring, drinking water supplied to customers remains clean and safe.
Utilities is fortunate to have two different water supplies. Several times this spring, the water treatment facility shut down its Poudre River supply to avoid heavy sediment- and ash-laden water. During these shutdowns, Utilities has the flexibility to rely on its other water supply from Horsetooth Reservoir. This redundancy allows water treatment facility operators to adjust or avoid undesirable water quality to continually produce the high-quality drinking water customers depend on. Additionally, Utilities monitors water quality before, during, and after the water treatment process to assure that clean and safe drinking water is delivered to its customers.