Pinto Lake Recreation Management & Public Health

Pinto Lake is a popular venue for many members of our community, as well as visitors from other cities, states and countries. Each year, thousands of people enjoy fishing, boating, sailing, duck feeding, bird watching and picnicking at the lake. Unfortunately, this 8,000 year old lake has a serious water quality problem.

Blue Green Algae Toxins

During the late spring, summer and fall months, Pinto Lake experiences heavy blooms of blue green algae (also known as cyanobacteria). Blue green algae blooms are an emerging health threat in the United States and many other countries. These blooms often produce toxins, which can be harmful to humans and animals. In humans, these toxins have caused skin rashes, nausea, bloody diarrhea and more serious conditions such as liver and kidney damage. There have been numerous reports of death in domestic animals and livestock due to drinking and swimming in waters with blue green algae blooms. A recent scientific paper showed that 21 southern sea otters in Monterey Bay died from exposure to blue green algae toxins. Pinto Lake was identified as a likely source of the toxins.

What Causes Blue Green Algal Blooms?

Pinto Lake’s blue green algal blooms are caused by high nutrient levels in the lake’s water and sediments. The City is currently working with the Environmental Protection Agency, State Water Resources Board, Central Coast Regional Water Quality Control Board, California Fish and Game and researchers from UCSC and CSUMB to identify the specific conditions that lead to bloom formation and toxin production. The City has received two grants totaling $225,000 for this important work.

Where Do the Nutrients Come From and What Can We Do To Control Them?

The elevated nutrients that drive the toxic algal blooms at Pinto Lake are probably coming from three sources in the lake’s watershed:

  • Accelerated erosion of naturally phosphate-rich soils
  • Septic systems
  • Agricultural operations

Over 99% of the lake’s watershed is in Santa Cruz County. As such, coordination and collaboration with Santa Cruz County on nutrient management and erosion control measures will be essential. Due to the complex nature of this problem, there is probably no “quick fix” solution. Effective control measures could include working intensively with local growers to manage erosion and fertilizer use and extending sanitary sewer services to all properties on Amesti Road. These measures will likely take years to implement and take effect. In the meantime, the City and Santa Cruz County will need to work together to manage the lake to protect public and environmental health.

Public Safety Management Measures

Currently, City staff monitors the lake for toxins on a weekly basis starting in spring when the first algal bloom typically appears. Weekly monitoring continues until toxins are detected. In most years toxins typically show up in May and carry on through November. When toxin levels exceed 1 part per billion (ppb) City staff posts warning notices (in English and Spanish) at the City park. This approach is consistent with current State guidance, which identifies an action level of 0.8 ppb to protect boaters and swimmers. It should be noted that while boating is allowed, swimming is prohibited at the City park. Santa Cruz County Health Department staff evaluated the situation and agree that posting is appropriate.

Based on data from the scientific studies, it is clear that toxin production in the lake is highly variable. Toxin levels can increase or decrease by as much as 1000-fold over the course of a few days. In addition, blue green algae can produce floating scum mats, which are driven by the prevailing winds and concentrate at the City park end of the lake. This can increase the concentration of toxins around the City launch ramp.

What About Fishing?

Fishing is a popular activity at Pinto Lake. During the summer and fall months (when toxin levels are typically highest), the majority of people do not consume the fish they catch. The Department of Fish and Game plants trout in the lake every winter (when toxin levels are usually low) and these fish are normally taken home and eaten. Given the fairly limited contact with water, the likelihood of significant exposure to toxins during actual fishing is probably low. However, it is possible that fish taken from Pinto Lake have toxins in their flesh. No tests have been conducted on fish from Pinto Lake, so the health risk associated with fish consumption is unknown.

The City of Watsonville will be working closely with Santa Cruz County on this issue with Pinto Lake.

For additional information on the Blue Green Algae, you can contact Robert Ketley, Senior Utilities Engineer at 768-3137.


This entry was posted on Tuesday, October 9th, 2012 at 11:51 am and is filed under City of Watsonville, Homepage News, Public Works . You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.