As part of ongoing biomonitoring, scientists from Metro Wastewater participate in an annual electrofishing program.  This monitoring program began in 1986 and there are currently thirteen sites spread over a forty-mile stretch of the South Platte River.  The same sites are sampled annually in the fall to compare historical data and change over time.  The main purpose of the program is to gather information on the species, size, quantity, weight, and health of the fish in Segment 15 of the South Platte River.  Various entities, including the Colorado Department of Public Health and Environment (CDPHE), use the data for river assessment studies, resegmentation, and habitat and aquatic life preservation projects.

CDPHE’s Water Quality Control Commission sets regulations to control surface water quality.  Regulation 38 establishes classifications and numeric standards for four rivers including the South Platte River and its tributaries.  Each river segment is assigned a stream classification, which may contain up to four designated uses including Aquatic Life, Recreation, Water Supply, and Agriculture.  Each combination of designations comes with ranges and standards for temperature, nutrients, and other parameters designed to protect these uses and meet the goals of the Clean Water Act ensuring every river segment is fishable and swimmable.

Colorado Parks and Wildlife (CPW) does regular fish surveys in the upper South Platte River drainage around the same time.  CPW and Metro sometimes survey at different times of the year for a specific study or construction project.   The National Park Service in conjunction with the US Fish and Wildlife Service surveys National Parks (like RMNP) rivers and creeks every year as well. Consultants may be hired to conduct fish surveys when projects take place in or near a body of water, such a building a bridge over a river, or destroying a pond for a parking lot.  For example, GEI Consultants performs surveys for clients all over the Western US using bank shockers (like MWRD) and backpack shockers. Some dischargers in South Dakota and Idaho are required by their states to monitor the instream fish populations, so they monitor upstream and downstream for fish, bugs, and habitat. Some participating entities have long-term data sets for some rivers going back 20 years, which is valuable information when observing the transitions of fish populations over time through weather events and flood years. Graduate students and researchers may also perform fish surveys as needed.

An electrofishing day begins by taking flow measurements.  The river flow must be below 300 cfs (cubic feet/second) on sampling days for safety concerns and accordingly, the flow is slow enough to successfully catch the fish once they are stunned.   Flags are placed along a 100-meter reach of the river to mark the sampling zone.  Two or three electrodes are connected together by power cords and held by members of the crew in the river.  These electrodes are on poles with a circular ring that is dipped into the water the entire time.  The electrodes are connected to a generator sitting in the back of a truck parked on the bank that is also attached to a cathode in the water to complete the circuit.  About 3-4 amps of alternating current hits the fish within about a 6-foot diameter area in the water.  The current temporarily paralyzes the fish much like a stun gun, thus making them easy to catch with nets.  Alternating current is used because it causes the least amount of harm to the fish and actually draws them towards the electrode so they do not float away too fast.  The amount of current will vary depending on the size of the river, flow, and conductivity levels of the water.