How extensive is CAP water quality testing at Lake Pleasant? Think 175 feet deep

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CAP's Bryant Dickens guides a multiparameter probe into the water at Lake Pleasant.

Near the New Waddell Dam at Lake Pleasant, the staunch 18-foot aluminum boat comes to a stop, then rocks gently over 175 feet of water depth. The deepest area of the lake.

Water quality will be measured every meter at this and four other locations on the lake.

At each location, Central Arizona Project (CAP) Water Resources Field Engineer Bryant Dickens will guide a multiparameter probe into the water to stop at each depth to record numerous constituents such as dissolved oxygen, pH, and water temperature, which from the crystal-clear surface to the pitch dark bottom this December morning, was a uniform 59-degrees.

CAP does not treat the water it delivers. Instead, it monitors water quality throughout the canal and reservoir system as a courtesy to cities and water utilities, who use CAP’s water quality data to help adjust their treatment processes before delivering drinking water to their customers.

After extensive measurements of the water column, Bryant recoils the cord and probe, yet another task in a stabbing winter cold.

The reason for the season (of sampling)

Water stored in Lake Pleasant, which also serves as CAP’s storage reservoir, comes from two main sources: The Colorado River via the CAP canal and runoff from the Agua Fria River.

CAP has been collecting water quality throughout the CAP system and Lake Pleasant since the late 1990s, including robust quarterly samples at Lake Pleasant that measure for more than 300 constituents. These measurements include a multitude of organic, inorganic, and synthetic constituents for which municipalities have expressed interest. A majority of these constituents are never detected in CAP water.

At the beginning of 2023, CAP expanded its sampling efforts in Lake Pleasant to include ten additional constituents. This expanded sampling supports water quality modeling efforts related to the System Use Agreement and guidelines for water quality standards for future introductions of wheeled non-project water.

CAP senior biologist Scott Bryan takes water samples at Lake Pleasant.
CAP Senior Biologist Scott Bryan samples water from Lake Pleasant

“We needed to beef up our data set and include Lake Pleasant in our overall water quality model,” said CAP Senior Biologist Scott Bryan, who supervised the efforts this day and bottled water samples to take to a local laboratory.  “One reason for testing monthly is to capture more of the ebbs and flows of the changing water quality.”

Bryan said the expanded monthly sampling efforts are geared toward the analysis of nutrients such as nitrates, phosphates, total dissolved solids, and total suspended solids that can contribute to the growth of algae and other organisms, which can either be harmful or beneficial to the canal.

This current phase of water quality testing will continue indefinitely, along with an expanding data set to support CAP’s water quality model.

Register for CAP University’s Feb. 21 deep dive on water quality

CAP created CAP University online learning opportunities in a continued effort to increase awareness and knowledge of CAP.

The public can learn more about Colorado River and CAP water quality for free at our deeper dive on CAP Water Quality and Monitoring online event from 9-10:30 a.m. on Wednesday, Feb. 21.

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