To celebrate World Water Day this week, we’re highlighting the San Lorenzo River’s water quality results from last year’s Snapshot Day! First held in 2000, Snapshot Day is the oldest and largest recurring volunteer water-quality monitoring event on a single day in California. Registration is currently open for the next Snapshot Day, to be held on Saturday, May 4, 2024!

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In 2023, 95 trained volunteers gathered on May 6 to monitor water quality across the four counties that border the Monterey Bay National Marine Sanctuary: San Mateo, Santa Cruz, Monterey, and San Luis Obispo. Their teams measured several water quality conditions in the field, and collected water samples that were analyzed in a laboratory for nutrients and bacteria.

Of the 77 sites with flowing water that could be assessed, less than a quarter (23%) met all of the targets, known as water quality objectives, for clean and healthy streams (down from 32% of sites in 2022).  The long-term monitoring conducted on Snapshot Day makes it possible to understand changes in the conditions of our rivers over time, and this information can be used to protect and improve steam health.

Three sites along the San Lorenzo River were monitored in 2023: at the river mouth, at the Highway 1 pedestrian bridge in Santa Cruz, and at Junction Park in Boulder Creek. Eight other locations were also monitored in the San Lorenzo watershed along three tributaries: three sites on Branciforte Creek, three sites at Carbonera Creek, and two sites at Zayante Creek. All sites are shown on the map below.

San Lorenzo River watershed sites sampled during Snapshot Day 2023. Map courtesy of Lindsay Brown, Monterey Bay National Marine Sanctuary

The measurement for pH, or acidity, did not meet water quality targets at all three San Lorenzo River sites and two additional sites in the watershed. These pH measurements fell between 6.3 and 6.75, which is more acidic than the desired pH range of 7-8.5. In addition, two sites on Carbonera Creek and one site on Branciforte Creek exceeded the objective for E. coli bacteria, and one site on Zayante Creek exceeded the objective for the nutrient orthophosphate (a form of phosphorous). All other measurements met water quality objectives across the San Lorenzo River watershed. The 2023 results are still an improvement over 2021, when the San Lorenzo River was labeled an Area of Concern based on the results of Snapshot Day that year.

You can read the full report for Snapshot Day 2023 here. Below, you can learn more about the different water quality parameters measured during the event, and see results for the San Lorenzo River sites. This information is from the Snapshot Day 2023 Final Report compiled by the Monterey Bay National Marine Sanctuary Foundation. We hope you’ll join us to monitor our rivers and streams for Snapshot Day on May 4, 2024!

Click here to read the Snapshot Day 2023 Report in full


Snapshot Day 2023 Results

 

Field Measurements

Dissolved Oxygen

Aquatic organisms rely on sufficient amounts of dissolved oxygen in the water to breathe and perform regular behaviors like feeding, spawning, and incubating. Excessive nutrients in the water can increase plant growth, which uses up dissolved oxygen once plants die and bacteria deplete the available oxygen as they decompose plant material. The water quality objective for dissolved oxygen is a value between 7 mg/L and 12 mg/L, which is considered an optimal range for cold-water fish.

During Snapshot Day 2023, all 11 sites in the San Lorenzo River watershed met the water quality objective for dissolved oxygen. San Lorenzo River measurements included 8.5 mg/L at the river mouth, 7 mg/L at the Highway 1 pedestrian bridge, and 9 mg/L at Junction Park.

 

pH

pH is a measure of the percent of hydrogen ions in the 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. The water quality objective for pH is a value between 7 and 8.5.

During Snapshot Day 2022, five of the 11 sites in the San Lorenzo River watershed did not meet the water quality objective for pH, including all three San Lorenzo River sites. San Lorenzo River measurements included 6.63 at the river mouth, 6.3 at the Highway 1 pedestrian bridge, and 6.5 at Junction Park. The other sites that did not meet the objective included Branciforte Creek above the confluence with the San Lorenzo River (6.75) and Zayante Creek at Quail Hollow Road (6.5).

Although it’s hard to know for sure what caused this drop in pH, the series of atmospheric rivers in the winter of 2023 could have brought slightly acidic rainwater to the watershed. The decomposition of organic materials is another possible cause (Lindsay Brown, Monterey Bay National Marine Sanctuary, personal communication).

 

Water Temperature

Just as the 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. The water quality objective for temperature is to not exceed 21 degrees Celsius (oC), which is considered an upper limit for the health of cold-water fish such as salmon and steelhead.

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. During Snapshot Day 2023, all sites in the San Lorenzo River watershed met the water quality objective for temperature. San Lorenzo River measurements included 13.5 oC at the river mouth, 12.5 oC at the Highway 1 pedestrian bridge, and 11.7 oC at Junction Park.


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. The water quality objective for E. coli is not to exceed 235 MPN/100 mL.

During Snapshot Day 2023, two sites on Carbonera Creek greatly exceeded the water quality objective for E. coli. These measurements included 1,262 MPN/100 mL downstream of the Camp Evers confluence and 25,994 at the Carbonera Creek bridge. In addition, the Branciforte Creek site above the San Lorenzo River confluence exceeded the water quality objective for E. coli at 432 MPN/100 mL.

All other San Lorenzo River watershed sites met the water quality objectives for E. coli. At the San Lorenzo River, these measurements included 92 MPN/100 mL at the river mouth, 104 MPN/100mL at the Highway 1 pedestrian bridge, and 170 MPN/100 mL at Junction Park (an improvement from 268 MPN/100 mL in 2022).

 

Nitrate as N

Nitrate (as N) occurs naturally 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 depletes the amount of oxygen available in a waterway when plants die off and bacteria decompose plant material. The water quality objective for nitrate as N is to not exceed 1.00 mg-N/L.

During Snapshot Day 2023, all eight sites in the San Lorenzo River watershed met the water quality objective for nitrate (as N). San Lorenzo River measurements included no detection at the river mouth, 0.1 mg-N/L at the Highway 1 pedestrian bridge, and no detection at Junction Park.

 

Orthophosphate as P

Orthophosphate (as P) is naturally occurring in streams and rivers; however, other sources that can contribute phosphate to waterways 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 depletes the amount of oxygen available in a waterway when plants die off and bacteria decompose plant material. The water quality objective for orthophosphate (as P) is to not exceed 0.12 mg/L.

During Snapshot Day 2023, the site on Zayante Creek at Mount Hermon and Bean Creek slightly exceeded the objective for orthophosphate (as P) at 0.13 mg/L. All other sites on the San Lorenzo River met the water quality objective for orthophosphate (as P). San Lorenzo River measurements included 0.05 mg/L at the river mouth, 0.05 mg/L at the Highway 1 pedestrian bridge, and no detection at Junction Park.

Read the full Snapshot Day 2023 report here!

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