A section of the Maple River channel measuring 7.6 m will be used for the natural setting. Measurements will be taken 2.5 m from the river bank, where the depth of the river ranges on average from 19.05 to 25.4 cm. The flume from the Stream Lab facility will be used as the laboratory setting to alter parameters measured in the natural setting. Three substrates (gravel, sand, and mixed gravel sand) will be used in each environment. An Acoustic Doppler Velocimeter (ADV) will be placed in the working section of the flume to make replicate depth profiles of velocity over each type of substrate. Measurements will be taken for five minutes, with two minute intervals in between replicates. A tripod will be used to hold the ADV in place within the water column, with the legs situated so the created wake will not affect the measurements taken. The sliding center column will be used to position the probe at the appropriate height above the substrate. The lowest height to be used will be consistent with the height of the sensory organs of a crayfish, approximately 4 cm. Additional readings will be taken at every two centimeters in height up to the water surface. Velocity measurements will be taken at a rate of 25 Hz for five minutes, which has sufficient signal resolution to resolve the inertial subrange of each habitat. Molecule dispersion from each type of pollution will be quantified using the chemical tracer dopamine coupled with an electrochemical detection system. Dopamine flow from a constructed reservoir tank will be regulated by in-line flow meter Simulated point source pollution will be introduced into the water column through plastic tubing. Simulated non-point source pollution will be introduced through plastic tubing with holes of varying diameter and spacing along the length of the tube. Each source of pollution will introduced at varying heights within the water column in replicate trials. A 30-µm triple C fiber microelectrode will be attached to the ADV probe, level with the sensor, with electrical tape. This will allow both the ADV and the microelectrode to be adjusted in tandem as height is varied. Molecule concentration and flow will be measured simultaneously at numerous heights about each of the three types of substrate. For each substrate type, plume concentration and velocity will be measured in depth profiles every 25 cm along the length of the flume. At each longitudinal position, five cross-sectional profiles will be taken.