On a recent Friday afternoon, retirees Christine and David Shima were enjoying the sunshine glinting off the waters of Ala Moana Beach Park.

The Shimas, of Halawa, were in town and decided to swing by and enjoy the beach, away from weekend crowds. Fortunately for them, the state Health Department had just removed signs warning of high bacteria levels for the central area of Ala Moana that morning.

Signs went up Wednesday and were removed Friday morning during the second week of January after testing determined the enterococci levels dropped from 1,013 to below the threshold level of 130 colony-forming units per 100 milliliters.

Members of the public can subscribe to email alerts for these advisories, but many, like the Shimas, were unaware.

Myron Honda, a supervisor for the department’s Clean Water Branch, said it was just a temporary spike, which is not uncommon for many beaches on Oahu’s south side. The department will not be investigating the source.

“When it spikes like this, there’s no way we can trace the source,” said Honda. “What we’re looking for is a continual discharge.”

Possible causes for a spike include leaking sewer pipes or waste from feral animals. The advisory was only for the central part of Ala Moana Beach Park, not the Diamond Head end or Magic Island.

“Our first priority is to inform the public,” said Honda. “We don’t close the beach. We’re just providing the public with information so they can make an informed decision as to whether they want to go in.”

In its advisory the Health Department warns the public that swimming at beaches with pollution in the water can cause illness, particularly among children, seniors and people with weakened immune systems.

But these swimming-­related illnesses are not usually serious, the department adds, and require little or no treatment, with no long-term health effects. The most common illness is gastroenteritis, with symptoms such as nausea, diarrhea and fever. Ear, eye, nose and throat infections can also occur.

Central Ala Moana, which the state tests weekly as part of routine monitoring, does not often test high for enterococci.

Since 2005, bacteria levels have exceeded the threshold only five times. The highest spike was in 2012, when 2,005 enterococci per 100 milliliters entered the ocean. The last spike was in July 2015, according to Honda, when it reached 192 enterococci per 100 milliliters.

That was before the state began issuing public water advisories online and posting signs in late 2016.

In November the Health Department revamped its website with new features in an effort to make the advisories more accessible to the public, with maps and an online email subscription service. Subscribers are also notified when an advisory has been canceled.

Honda says he’s received positive feedback from the city Ocean Safety and Lifeguard Services Division and tourism representatives, which the department works with to keep the public informed. Lifeguards are sometimes the first to report brown water following heavy rain, while the city informs the state of sewage spills.

Honda would like more people to subscribe to the advisories. As of December there were only 171 subscribers.

Down the line, the department hopes to make water advisories available via text message.

The Surfrider Foundation, a longtime advocate for better beach water quality monitoring and public notification, has been working with the Health Department for years to improve its system.

Marvin Heskett, Surfrider’s water quality specialist and a chemist, said a decade ago the data was available to the public online but was difficult to find. Also, the Health Department was not consistently posting signs at beaches.

Surfrider offered to host the data on its website to make it more accessible, and eventually helped the state secure funds for an annual Environmental Protection Agency BEACH Act grant. For this fiscal year the Health Department received $265,000 to operate the program.

Heskett said the department is making progress with its revamped website but still has plenty of work to do.

Of the approximately 450 beaches statewide, the Clean Water Branch tests 160.

On Oahu, 23 sites are considered “Tier 1” sites that are popular and are tested weekly. Among “Tier 1” beaches are Ala Moana Beach Park and Magic Island, as well as Kailua and many beaches in Waikiki.

Other beaches, considered “Tier 2,” such as Ewa and Fort DeRussy Beach Park, are less frequently visited and not as susceptible to pollution. They are tested monthly or every other month. “Tier 3” beaches are not routinely monitored.

Troy Maeda is one of two environmental health specialists from the Clean Water Branch who collect water samples throughout Oahu. There are two working on Oahu and one each on the Big Island, Maui and Kauai.

As part of his routine, he wades in knee-deep at Tier 1 sites such as Magic Island, and fills a bucket with water. He transfers some to a bottle, to be transported on ice to the lab in Pearl City within six hours, and tests the rest for a variety of properties, including acidity, turbidity and dissolved oxygen.

The samples take 24 hours to process at the lab. Once results are confirmed, advisories are issued online.

While the branch tests for several indicators, including the germ clostridium perfringens, it posts advisories only for high levels of enterococci as an indicator of pathogens as required by the EPA. Results for other bugs are available on its website.

Some areas, such as Kahaluu and Keehi lagoons, have permanent signs posted because of the consistency of high bacteria levels.

Permanent signs have been posted since at least 2014 at Kahaluu Lagoon and since 2016 at Keehi Lagoon.

Honda said regular sampling results at Kahaluu helped the state determine that cesspools were contributing to high counts in the watershed. Keehi Lagoon, a popular spot for paddlers, has consistently high levels of enterococci, he said, due to several streams that empty into it. Signs are also permanently posted at the Ala Wai Canal.

A handful of other sites on neighbor islands are being considered for permanent signs as well, said Honda, who declined to disclose their locations.