Thanks to assistance from the Lodi Fire Department and their fire rescue boat, the City of Lodi Storm Drain Detectives were able to measure the water clarity in Lodi Lake and the Mokelumne River to help celebrate July as the National Lakes Appreciation Month. The findings will be included with data collected during the 2023 Annual Secchi Dip-In, a nationwide volunteer waterbody monitoring event. This marks the twenty-third year that Lodi has participated in the nationwide event.
What is a Secchi Disk Dip-In? The concept is simple. Individuals use a Secchi disk, an 8-inch metal disk with alternating black and white quadrants, and lower it into a lake, stream, river, or other body of water documenting the depth at which the disk is no longer visible. The depth of disappearance is called the Secchi depth measurement and it measures the transparency, or clarity, of the upper water column.
Turbidity is the cloudiness in water caused by large numbers of individual particles that are generally invisible to the naked eye, like smoke in the air. The measurement of turbidity is a key test of both water clarity and water quality, which can determine the health of the water.
The Mokelumne River and Lodi Lake’s watershed includes runoff from the City of Lodi’s streets during wet or dry season. Rainy season, or dry season street stormwater runoff, is often a “non-point source of pollution” which can include car oil, grease, fertilizers, detergents, pesticides, garden soil, and other contaminants, coming from homes, parking lots, streets, garden landscapes, making it very hard to trace back to the original source for containment. To some degree, we all contribute to the pollution problem. Please remember, “Only rain down the storm drain!” and “We are the solution to water pollution.”
The measurements taken by the Storm Drain Detectives on July 11 were collected mid-day from three different sites. Site One, Lodi Lake West, north of the boathouse, measured water clarity at 5.9 feet. Site Two, Lodi Lake East, measured water clarity of 5.9 feet. The lake swimming and paddling activity was minimal. The weather was calm. The team noted that Lodi Lake’s clarity was severely impacted by plant growth at the lake bottom. Site Three, in the main Mokelumne River channel, about 500 feet above the Woodbridge Irrigation District Dam, measured water clarity at 10.1 feet. There was no evidence of plant growth in the river bottom and no paddle or kayaking activity nearby, though the current was swift, with Camanche Dam Reservoir releasing water at 1998cfs. Water temperature in the Mokelumne River below the Woodbridge Dam was 63 degrees (F), compared to Lodi Lake water temperature measuring 68 degrees (F).
Lodi Lake’s visible water quality has not significantly changed since monitoring began in 2001, though water weeds have increased. Conversely, the Mokelumne River’s water clarity seems to fluctuate depending on whether there has been high rain and snow runoff or drought conditions during the year. This year’s high flows have swollen the riverbanks and increased turbidity somewhat.
To learn more about water quality, the City of Lodi’s Storm Drain Detectives (SDD), or the 2000-2023 SDD Mokelumne River monitoring data, see: https://www.lodi.gov/492/Storm-Drain-Detectives