Since Earth Day 2000, volunteers have assembled on the first Saturday morning of May each year to collect water quality samples from water bodies that enter the Monterey Bay National Marine Sanctuary. This decades-long data set has become a valuable source of water quality data for the region, allowing long-term comparison across the years.
In 2021, 67 volunteers trained and organized by the Monterey Bay National Marine Sanctuary and California Marine Sanctuary Foundation monitored 75 sites with sufficient water flow to collect samples. Of these, 31% met all Water Quality Objectives (WQOs) meaning that the water bodies were clean and healthy in these locations.
When a site does not meet three or more Water Quality Objectives, the site is listed as an Area of Concern. Four sites on the San Lorenzo River were monitored this year and two of those exceeded three or more Water Quality Objectives, placing it on the list as an Area of Concern. This is the second time that the San Lorenzo River has been on the Area of Concern list since 2000.
Below, you can learn more about the different water quality parameters measured and how the San Lorenzo River sites stacked up. The information below is from the Snapshot Day 2021 Final Report compiled by the Monterey Bay National Marine Sanctuary Foundation.
Click here to read the Snapshot Day 2021 Report in full
Field Measurements
Dissolved Oxygen
Aquatic organisms rely on sufficient amounts of dissolved oxygen to perform regular behaviors like feeding, spawning and incubating. Excessive nutrients in water can cause an increase in plant growth which uses up oxygen in the water once plants die and bacteria deplete the oxygen available to aquatic organisms as they decompose plant material.
During Snapshot Day 2021, the San Lorenzo River mouth did not meet dissolved oxygen WQO.
pH
pH is a measure of the percent of hydrogen ions in water. A value of 7 is neutral, above 9 is alkaline (or basic) and below 5 is acidic. Many aquatic organisms require a very specific pH range to carry out necessary chemical and biological reactions; extremely low or high pH levels impede essential functions for survival or damage tissues.
During Snapshot Day 2021, the San Lorenzo River at Henry Cowell State Park did not meet the pH WQO.
Water Temperature
Just as temperature on land impacts terrestrial plants and animals, the temperature of the water can affect the life and health of aquatic organisms. Many fish species and other aquatic life need specific temperature ranges within which to survive and reproduce. Water temperature can also affect the amount of dissolved oxygen with higher temperatures causing a decrease in dissolved oxygen. Slowing water flow or removing streamside vegetation which provides shade can also cause water temperatures to rise to undesirable levels that may harm aquatic life.
Snapshot Day data is collected during the morning hours, so water temperature measurements do not necessarily reflect the maximum daily temperatures for the water body. In 2021, all Snapshot Day sites met the water temperature WQO.
Lab Analysis
E. coli bacteria
Coliform bacteria generally originate from the feces of warm-blooded animals such as humans or wildlife. While coliform bacteria are usually not the cause of sickness, their presence can indicate that other illness causing pathogens are present.
During Snapshot Day 2021, the San Lorenzo River at the mouth and Highway 9 did not meet the WQO for E. coli.
Nitrate as N
Nitrate (as N) is naturally occurring in streams and rivers, however other sources that can contribute nitrate to creeks and rivers include fertilizers, pesticides, detergents, animal waste, sewage or industrial wastes. Heightened levels of nutrients can lead to excessive algal or aquatic plant growth which ultimately deplete the amount of oxygen available in a waterway when plants die off and bacteria decompose plant material.
In 2021, the Snapshot Day sites along the San Lorenzo River met the nitrate as N WQO.
Orthophosphate as P
Orthophosphate (as P) is also naturally occurring in streams and rivers, however other sources that can contribute phosphate to creeks and rivers include fertilizers, pesticides, detergents, animal waste, sewage or industrial wastes. Heightened levels of nutrients can lead to excessive algal or aquatic plant growth which ultimately deplete the amount of oxygen available in a waterway when plants die off and bacteria decompose plant material.
During Snapshot Day 2021, the San Lorenzo River at the mouth and Highway 9 did not meet the Action Level for orthophosphate as P.