The unprecedented absence of visitors to Hanauma Bay Nature Preserve due to coronavirus concerns has offered researchers a rare opportunity to study the impact of humans on the county park’s diverse marine life.

The only people who’ve been allowed on the famous beach in the last five months are a small number scientists, who on Friday reported that they have found larger fish, more monk seal activity and clearer water during the COVID-19 pandemic.

The water in the nature preserve is now more than 40% clearer than when the park was receiving thousands of visitors per day, according to preliminary observations comparing water quality during the pandemic to data from two years ago.

The water is also clearer by 18% than it was on Tuesdays, the one day of the week when the park has historically closed to give the natural environment a one-day breather from human activity.

The nature preserve has been closed since March 18, 2020. Since then the number of daily visitors to Hawaii’s premier snorkeling destination has sunk from 3,000 to virtually none.

Maintenance and upkeep of the facilities has continued during the closure, including planning for renovations of the sewage system, replacing invasive plants with native flora and bathroom improvements.

There is no set public reopening date.

Across Hawaii, concerns over the impact of recreational activities such as swimming, diving and snorkeling on fragile marine ecosystems have increased over the decades with the astonishing growth of the state’s tourism industry.

But it’s been difficult to study the relationship between the mobs of people recreating in nearshore waters and the various forms of environmental degradation that scientists are documenting, especially when there are so many other factors at play — rising ocean temperatures, coral bleaching and stormwater runoff, to name a few.

Now that scientists have a rare chance to study changes to the marine environment with zero human impacts — and then again when the park is repopulated by thousands of visitors per day — it will be much easier to draw out a cause and effect.

Previous research at Hanauma Bay suggests that human disturbance contributes to coral breakage, as well as the loss of entire coral colonies.

Researchers also suspect that recreational activity at the bay impacts fish feeding behaviors.