Eleven-year-old Anthony Rosales reels in a black and white secchi disk as 12-year-old Ryan Solda watches for it to come into focus through the lake water.
"I see it," Solda said as the disk was 6.6 feet deep in the water.
The two boys were helping Kathy Grant conduct a test to measure the lake's clarity.
Once a year for the last decade, Grant, the city's watershed education coordinator, has tested the clarity of Lodi Lake and the Mokelumne River. It is part of a national effort to monitor how people are affecting bodies of water.
During the past two years, Grant has had the help of the Outdoor Adventure Club. It is a city-sponsored three-day summer camp that takes place every week for kids who want to kayak, take nature walks or ride down the river on a boat.
"We are letting their own natural curiosity teach them," counselor Chris McGeorge said.
Lodi Lake's clarity decreased from last year, although 2010 was the clearest the water has been in the last decade Grant had measured the lake.
Suspended sediments, plant life, salts, dirt, pollution and other runoff materials can affect the clarity of the water. A decrease in transparency could point to an increase in urban and agricultural runoff, Grant said.
Rosales said it is disappointing to see the clarity decrease because he often comes to the lake with his family.
"A lot of people are being careless and not taking their trash to the recycling bin and are instead dumping it in the lake," he said.
The boys tested the water in two locations on the lake and one on the river. They take turns dropping an 8-inch black and white disk known as a secchi into the lake, and recording the depth at which the disk is last visible before it disappears into the water.
Nine-year-old Liam McLoughlin said he took kayaking lessons last year and enjoys being out on the river because he discovers new things, like turtles and otters.
"I thought the water would be cleaner because we are all trying to help out to make our Earth cleaner," he said.
If the clarity of the lake keeps deteriorating, Solda said he is worried about the future of the lake.
"It's a really pretty lake and people come here for nature. If people keep throwing in their trash, it will get dark and not be as naturey anymore," he said.