Lodi, Calif. – August 4, 2021 – July was National Lakes Appreciation Month and on Thursday, July 15, a group of volunteers known as the Storm Drain Detectives dropped a Secchi disk into Lodi Lake and the Mokelumne River to measure water clarity. The findings will be included with data collected during the 2021 Annual Secchi Dip-In, a nationwide volunteer waterbody monitoring event. This marks the twenty-first 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 as 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 columns.
Water clarity is one measurement that is used to determine the health of a body of water. The City of Lodi’s storm water, which includes rain and landscaping runoff, drains into Lodi Lake and the Mokelumne River untreated. Transparency can be impacted by suspended sediments, algal abundance, and potential pollutants in the water. Suspended solids often come from plant nutrients that enter the water through local urban runoff, construction sites, and local agricultural fertilizer or animal waste. Summer street runoff can be potentially loaded with herbicides, pesticides, and detergents from car washing. Please remember, only rain goes down the storm drain!
The measurements taken by the Storm Drain Detectives on July 15 were collected mid-day from three different sites, two sites in Lodi Lake and the third in the Mokelumne River, upstream of the Woodbridge Irrigation Dam (WID). Site One, Lodi Lake West, north of the boathouse west of center of the lake, measured water clarity at 7.6 feet. Site Two, Lodi Lake East, east of the lake’s center, measured water clarity of 5.8 feet. Site Three, Mokelumne River/Upstream of WID Dam, in the main channel approximately 500 yards upstream from the dam, measured water clarity at 8.4 feet. The kayaking and paddle boarding activity on the lake on Thursday most likely contributed to the decrease in water clarity, while water conditions on the river appeared calmer with higher water clarity. Also of note was the increased presence of plants growing from the bottom of Lodi Lake.
Lodi Lake’s visible water quality has not significantly changed since monitoring began in 2001. Conversely, the Mokelumne River’s water clarity seems to fluctuate over time depending on whether there has been high rain and snow runoff or drought conditions.
Data from 2001-2021:
Learn more about the nationwide Annual Secchi Dip-In at: https://www.nalms.org/secchidipin/about/history/
Learn more about Lake Appreciation Month at: https://www.nalms.org/lakes-appreciation-month/
Press Release [PDF]