Right now, we are coming down from the spring runoff and anglers are wondering if their local rivers and streams are ready for fishing again. For the most part, yes, rivers and streams across the state have retreated from the spring highs and are settling into more consistent summer flows fed by the remaining snowpack and groundwater. A useful resource for determining if the conditions are right to get back on the water, in a boat, or in the water, in waders, is to check in with the U.S. Geological Survey's (USGS) stream gauges. The USGS has measured streamflow in rivers and streams across the country for more than a hundred years. Stream gauges are useful for many purposes, however, they can be particularly helpful for fly anglers. Streamflow is a computed figure that is derived from discharge and gauge height measurements collected at a gauge. For anglers, streamflow can provide us an idea of the conditions of the water and help us prepare where to go and what flies to bring along. To make streamflow data useful, you must know some background information about the river or stream. Is it big water (i.e. the lower Arkansas) or a stream traversing a narrow canyon (i.e. Clear Creek)? The ideal conditions may be very different from one river to the next. Therefore, streamflow needs to be put into context. For reference, the USGS provides a useful indication on streamflow graphs to inform the reader how the current reading compares to historical data (as indicated by yellow triangle). For example, on 7/1/2020, the daily discharge value on the Colorado River below Glenwood Springs was 3870 cubic feet per second, while the median value for historical July 1st data was 7,800 cubic feet per second. Therefore, this information is telling us that there is significantly less water flowing through the Colorado River at this time. Likewise, the value for Clear Creek at Golden, 366 cubic feet per second, is far below the median, 624 cubic feet per second. What does this information mean for anglers? Low stream flows can impact the behaviors of fish and determine the best techniques to catch fish. When water streamflow is low, particularly in the heat of summer, water temperatures are likely to rise, pushing fish into pools and deeper water. When streamflow is high, the quick moving and sediment filled water will make it difficult for fish to see flies on top or even below the surface. Anglers should seek out the slower water pockets and use large attractor flies to get the attention of fish. Streamflow data, like climate information, weather, and fish biology is an additional tool that can help anglers do what they love, catching fish.