A group of catch-and-release fishermen wading the South Platte River met with unusual success Thursday morning, catching bucketfuls without casting so much as a single line.
    Instead, these anglers used low-level electrical current to net their prey and all in the interest of promoting river health.
    As part of its annual fish survey Metro Wastewater Reclamation District scientists took to the riverbed and captured a variety of species in order to get data on each type of fish. Their methods, though unorthodox by sport fishing standards, are a clever and humane way to get fish counts without harming the specimens, according to Metro Wastewater spokesman Steve Frank.

    Augmented by some highly specialized electronic gear and a small electrical power generator, the river itself becomes part of the capture apparatus. The running river water provides the conductance necessary to complete a circuit between electrodes (anodes) and a cathode placed in the river. Fish in the river near the anodes are stunned and float to the surface where the scientists, who identify them by species, measure, and weight before returning them to the river, collect them.  The team looks specifically at two things: how many species they can find (both native and non-native) and how many total fish in the catch. 
    “Ideally, we will find strong numbers of fish along with strong diversity, but that can change depending on the habitat available to the fish,” Frank said. “We typically find between 10 and 20 species per site with wide ranging numbers.  Most of the fish we do find are native, including the Johnny Darter and the Longnose Dace.  The continuous presence of these individuals gives us a strong indication that the South Platte is fulfilling its role as a healthy habitat for aquatic life.”
    In addition to the fish survey, the scientists also conduct macroinvertebrate, or insect, surveys.  Taking to the river again, the team looks for bugs in two habitats, along the bottom and banks, and in the vegetation.  To assess the macroinvertebrates on the riverbed, scientists place a small-mesh net into the water downstream of a riffle, or shallow, high turbulence portion of the stream.  Disturbing the sediment the team attempts to dislodge any macroinvertebrates from their habitat.  They collect the samples from the net and preserve them in alcohol until they can be counted and identified by professionals. 
    A similar process is used to assess macroinvertebrates along the banks.  The types and numbers of different macroinvertebrates can indicate ecosystem health, according to Frank. 
    “Using a method developed by the state health department, we can calculate a ‘jingle’ that indicates whether or not a segment is impacted or not,” Frank said. “Unfortunately, we cannot distinguish between the effects of poor habitat or poor water quality based only on the score. This is part of the reason why we sample many places along the river. Macroinvertebrates also provide food for other animals higher in the food chain. Like the fish survey, it’s another tool we use to assess the health of the River.”
     The surveys, conducted along about 40 miles of river from 31st Street in Denver to Weld County Road 32.5 in Platteville, pulls samples from 11 locations on a yearly basis. With the addition of a location a few hundred yards south of WCR 4, the team hopes to get ahead any potential pitfalls with upcoming district expansion plans.
    Jim Dorsch, water quality officer for MWRD, explained the goal of the team’s assessment at the new site, just downstream of where the district is building a major new treatment facility.
    “Our job starts at the discharge, and upstream and downstream from the discharge, making sure we are not in any way negatively impacting the community,” Dorsch said. “That is what we are doing here. We have an opportunity with the new Northern Treatment Plant to come in and get five years worth of baseline data as to what’s here now, and what’s going on in the river, and compare that to when the new plant comes on line.”