Snowpack functions like a natural reservoir—storing water through the winter and releasing it gradually as it melts. But the below-average snowpack and precipitation during the 2025–2026 winter provided less water to sustain streams and replenish reservoirs through the warmer months.

Drought in the headwaters can affect everyone throughout the system—from headwater users and senior water-right holders, to those with junior rights who may face reduced supplies, communities and ecosystems that depend on return flows, and downstream users trying to fill their reservoirs.

The next step in water's journey is runoff—the water that flows from the mountains into streams and rivers. Tributaries are the streams and creeks that feed the Blue River, including Snake River and Tenmile Creek, carrying water from the surrounding mountains into the larger river system. Their flows are influenced by snowmelt, precipitation, groundwater, and weather conditions.

Tributary flows provide an early and localized picture of water availability across the watershed. When tributaries are running low, less water is available to flow downstream, fill reservoirs, support ecosystems, or meet the needs of water users. Conditions can vary considerably between tributaries, making individual streamflow measurements important for understanding what is happening across the watershed.

Streamflow is the amount of water flowing past a specific point in a stream, typically measured in cubic feet per second (cfs). Comparing current streamflow with historical averages helps show whether rivers and tributaries are running wetter or drier than normal and provides important information for understanding current water-supply conditions.

Reservoirs provide large-scale storage, allowing water managers to capture water during wetter periods and control releases to meet water needs during drier periods.

Dillon Reservoir collects and stores water from the Blue River and its tributaries, making it a critical link between the Upper Blue River Basin and the larger Colorado water system. Water entering the reservoir can be stored, released downstream, or diverted through the Roberts Tunnel to the South Platte Basin to supply Front Range communities.

Dillon Reservoir is an important point of connection—and competition—in the watershed. The amount of water flowing into the reservoir, the amount stored, and the amount released or diverted all influence how much water remains in the Blue River downstream and how much is available to meet needs elsewhere. During drought, these decisions become more consequential as water supplies become limited.

Reservoir storage measures how much water is held in Dillon Reservoir at a given time, while inflow measures how much water is entering the reservoir. Comparing current storage and inflows with historical conditions helps show how much water is available and how drought is affecting the system. In drought, managers must draw down Dillon Reservoir due to the lack of replenishing supply from snowpack and precipitation.

From Dillon Reservoir, water either continues downstream in the Blue River or is diverted through the Roberts Tunnel toward the South Platte Basin on the other side of the Continental Divide.

The Blue River carries water downstream from its tributaries and Dillon Reservoir toward Green Mountain Reservoir, connecting communities and water users along the way. Its flow depends on snowmelt, precipitation, tributary inflows, reservoir operations, and water diversions.

What happens in the Blue River matters both locally and downstream. River flows support communities, agriculture, recreation, and aquatic ecosystems, while also providing water that ultimately reaches Green Mountain Reservoir and the larger Colorado River system. During drought, reduced flows can put pressure on water users and ecosystems throughout the watershed. Monitoring streamflow helps us understand current conditions and informs water supply and environmental management.

The Blue River ultimately carries water toward Green Mountain Reservoir, where local water supplies become part of an even larger network of storage, water rights, and downstream demands.

Green Mountain Reservoir is a critical link between the Blue River watershed and the larger Colorado River system. Water flowing downstream through the Blue River enters the reservoir, where it is stored and managed to meet the needs of multiple water users, including those who rely on the Historic Users Pool (HUP).

What happens at Green Mountain Reservoir can have implications far beyond the reservoir itself. Storage, inflows, and releases affect downstream water users, agriculture, communities, ecosystems, and the amount of water that continues into the Colorado River. During drought, limited inflows and storage can make balancing these competing needs increasingly difficult.

Reservoir storage and inflow provide important measures of the system's water supply. Comparing current conditions with historical averages helps show whether Green Mountain Reservoir is receiving and storing enough water to meet the needs it was designed to serve. In drought, managers must draw down Green Mountain Reservoir due to the lack of replenishing supply from snowpack and precipitation.

For the first time in its history, Green Mountain Reservoir did not have sufficient supplies in 2026 to fully serve the Historic Users Pool.

From Green Mountain Reservoir, the water journey continues into the Colorado River, connecting the Blue River watershed to water users and communities throughout the Colorado River Basin.