BOISE, Idaho — The City of Boise is working to understand if fish in the Boise River are being impacted by people. When water leaves the wastewater treatment facility and re-enters the river, the temperature is much warmer than the river water. That led the city to conduct a study to see if fish are affected by these warmer waters.
"People come from all over to fish this river," said Sampling and Monitoring Supervisor of the Water quality Division of the Boise Public Works Department, Dorene Macoy. "So we have two wastewater renewal facilities where we treat effluent that comes from the city and industries into our facilities."
Fish can be affected by a lot of different conditions in local rivers, such as water quality, flow rates and even water temperatures can all play a part in fish health. With this study, crews will be able to definitively say if warmer water near the Boise wastewater treatment plant is affecting the fish in the Boise River.
Macoy said the water renewal process heats up the water. In general, the water that is discharged is 10 to 20 degrees warmer than the river water upstream. When the discharge and river water combine and flow downstream it amounts to 1 to 3 degrees of warming in the river.
"So, with this study, we want to make sure that that water that clean water, that's a little bit warmer than the river is not acting as a fish barrier," Macoy said.
The key to this study is being able to track the movements of the fish in a stretch of the river just west of Boise. Crews caught and tagged fish to be able to see where they swim. The fish were caught using an electro-fishing technique.
"It creates a field of electricity that the fish are drawn to," Macoy said. "Then they're stunned and we net them."
Macoy said this method is safer for the fish than if crews caught them using nets, since the fish are handled less. The fish are then weighed, measured, identified and prepared to be tagged.
"Before we even start handling the fish, the fish have a spa day," Macoy said. "We have peppermint oil that we put in the water, that makes them very, very mellow. We tag them in their belly cavity, with a two millimeter tag."
She said the more mellow the fish are, the less they fight, and the easier this process is on their bodies. Once the tag is inserted crews check to ensure it is working. The fish are then put back into the water.
Each tag has a unique ID number that will be detected by radio equipment that is near the discharge site of the wastewater treatment facility. The fish swim away but now crews can see where they go.
"It just registers that number, and then that is transmitted to a box and records that data," Macoy said. "Every time a fish approaches this equipment, crews will be able to confirm that fish downstream of the wastewater treatment plant can swim past the warmer waters, and continue upstream."
By collecting that data, they can prove that the warmer water is not blocking the fish passage, thereby showing that the wastewater is not affecting the fish in the river.
The study is expected to run 2 years, but is subject to change.
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