Partnered with the Old Gallery in Allenspark, CO, the Rocky Mountain Conservancy is again hosting the Science Connections Speaker Series in 2025. This series is open to the public and offers a chance to learn about current research taking place in Rocky Mountain National Park.
On Tuesday, August 19th, Katie Gannon, a PhD student at the University of Colorado Boulder, presented “Are Filamentous Algal Blooms Changing Mountain Lakes?” Gannon shared her end of summer report from the research she conducted at alpine lakes in Rocky as part of the CU Boulder Mountain Limnology Lab. This research was supported in part by a grant from Rocky Mountain Conservancy.
During the summer of 2025, Gannon and her team collected over 140 water samples, gathered over 27,000 data points from high frequency data sensors, and hiked over 80 miles to get closer to the answers of why filamentous algal blooms are occurring in Rocky’s lakes and how are they impacting aquatic ecosystems.
When people think of alpine lakes, pristine, sparkling blue water at the base of stunning geological features often comes to mind. These high mountain lakes are characterized by cold water, a short growing season, and a small watershed with minimal nutrient input. These factors limit plant and algal growth and allow them to retain their distinctive blue color. It also makes them crucial indicators of environmental change. The conditions inside a lake are not just dictated by natural processes, but also pollutant sources such as the burning of fossil fuels and the use of fertilizer and pesticide. These processes release pollutants into the atmosphere that are then deposited in remote locations, such as alpine lakes.
“Because mountain lakes are sensitive indicators, integrators of everything going on around them, and getting nutrients from the atmosphere, they are the perfect laboratory to understand how changes in environmental and air quality can impact ecosystem processes,” said Gannon.
For the past 40 years, the Loch Vale Watershed Program, a long-term ecological research and monitoring initiative, has studied how changes in water and air quality impact The Loch, Sky Pond, and other key lake ecosystems in the park. Long term data can help researchers identify slow, long-term changes over time as well as novel events that have occurred.
In 2010, Loch Vale watershed researchers noticed that nearshore areas of some alpine lakes in Rocky were turning green. If mountain lakes are supposed to be blue, why are some green? This shift occurs when eukaryotic single celled organisms commonly known as algae carry out photosynthesis the same way terrestrial plants do. Sunlight, water, nutrients, a happy temperature, and time allow life to grow, leading to greener lakes.
The source of the green color was identified as filamentous algal blooms (FABs), which are long strings of photosynthesizing organisms that grow in nearshore, shallow areas of lakes. These littoral zones are “prime real estate for algae,” said Gannon. “The water is shallow, warmer, and nutrient-rich.”
In order to see if this was a new occurrence, Gannon’s lab collected samples from the bottom of Sky Pond and The Loch and analyzed each layer of sediment to identify changes over time. In both lakes, they found unprecedented changes in algal communities since the 1950s, with an increase in algal growth linked to changes in nutrient availability and temperature in lakes. However, this isn’t just happening in Rocky. “It’s part of a larger pattern of nearshore blooms happening in low nutrient lakes around the world,” said Gannon.
Changes in algae content at the base of an aquatic food web can lead to changes up the chain to birds and fish. To learn how these blooms are impacting the aquatic ecosystem, Gannon is comparing areas in lakes with FABs to areas nearby without them, with most of her research focused on The Loch and Sky Pond.
The first primary research method was collecting water samples at multiple points across both lakes, including both near shore areas with and without FABs. These samples are processed in a lab to find out how much organic matter is in the water. Gannon’s team also installed high frequency sensors in the lakes as another research method. These electronic instruments sit in the water all summer and collect temperature and oxygen data points every few minutes. “Things grow faster in warmer water and algal cells produce oxygen when they photosynthesize,” said Gannon. “If we look at changes in oxygen over time, we can also see what growth looks like.”
The preliminary results from the research conducted during the summer of 2025 showed an increase in nutrient concentrations in areas that have FABs compared to areas that do not have them. “We are also seeing a much higher concentration of particulate organic matter in areas with FABs than areas without them,” said Gannon.
Next steps for Gannon and her lab will be to look at how algal blooms impact wider ecosystems and food webs within Rocky’s lakes. The data points collected from the high frequency data sensors will also be used to understand how these blooms are impacting concentrations of oxygen in near shore areas of lakes.
“Long term data is really important,” said Gannon. “It allows us to know what kinds of questions to ask and put patterns into context.” Rocky Mountain National Park is a special place worth understanding and studying, and research like that being conducted by the CU Boulder Mountain Limnology Lab will help keep deepen our understanding of the changes and challenges facing Rocky’s alpine lakes so that we can more effectively work to keep them pristine for future generations.
