City of Lodi marks its 20th annual Secchi Disk Dip-In

Every summer for the past two decades, the City of Lodi’s Storm Drain Detectives program has marked the annual Secchi Disk Dip-In.

On July 13, the group’s adult leaders took up the task that normally falls to students in Lodi Unified School District, marking year 20 of participating in the citizen science project to collect water quality data. Due to the COVID-19 pandemic, the students were unable to participate this year.

Just after noon, the leaders dropped a Secchi Disk into the water at various sites at Lodi Lake and the Mokelumne River. Then, they recorded their results.

The concept of the DipIn is simple. Testers lower a Secchi disk — an 8-inch metal disk with alternating black and white quadrants — into any lake, river, stream or other body of water until they can no longer see it. The depth at which the disk disappears is carefully noted. Called the Secchi depth measurement, this measures the transparency and clarity of the water.

Water clarity can help indicate if a body of water is “healthy” or “unhealthy.” In the case of Lodi Lake and the Mokelumne River, stormwater and other runoff drains to the lake and river year-round, and the Secchi Disk Dip-In helps the city to monitor the effects of that runoff.

Lodi’s measurements were taken from three sites, two on Lodi Lake and one on the Mokelumne River, just upstream of the Woodbridge Dam.

On the western site at Lodi Lake, north of the boathouse, the Secchi depth measurement was 8.8 feet, while the disk was visible to 6.4 feet on the center/east side of the lake. The water was clear to 7.8 feet on the Mokelumne River.

Transparency can be affected by the color of the water, suspended sediments, algal abundance, and potential pollution in the water. Summer street runoff can be potentially loaded with homeowner’s herbicides, pesticides and soapy water from car washing.

Lodi Lake’s visible water quality has not significantly changed since monitoring began in 2001. However, the river’s water clarity seems to fluctuate over time, depending on whether there have been large amounts of rain or snow runoff, or drought conditions.

The Storm Drain Detective leaders also noted the increased presence of water plants growing from the bottom of Lodi Lake.

The Dip-In is an international effort in which volunteers produce a “snapshot” of the transparency of water across the United States and Canada. Sponsored by the North American Lake Management Society and the United States Environmental Protection Agency, the Dip-In is directed by former Kent State University scientist Dr. Robert Carlson.

Since the Dip-In began in 1994 in six Midwest states, it has expanded to include data gathered by more than 400 programs and 9,000 volunteers.

For more information, visit www.nalms.org/ secchidipin. July is also Lake Appreciation Month; for information and events, visit www.nalms.org/events.