A new dye test shows wastewater from public restrooms at a North Shore beach park is reaching the popular Shark's Cove tide pools within days, which is bad news for the hundreds of people who swim there daily.

• Researchers poured harmless green dye down the park's restroom drains, and within two to three days it showed up in the tide pools in high concentrations.
• The dye was strongest right below the lifeguard stand near the bathrooms, and one reading maxed out the measuring instrument, pointing to a direct path from the septic system to the ocean.
• Two to three days is not enough time for soil microbes to break down pathogens or nutrients, so the water reaching the ocean is essentially raw wastewater.
• The park's septic system does some basic treatment, which is better than the cesspools common around North Shore beaches, but it still lets much of the waste through.
• The state Health Department will review the study but says it relies on its own monthly testing to decide on swimming advisories, while a volunteer group also tests the spot twice a month.

Outlook: The city parks department plans more nearshore water testing to decide if cleanup is needed and is exploring wastewater system upgrades, though any fix is likely years away.