Hanauma Bay Nature Preserve Park is one of the crown jewels among city parks; a panoramic view of the bay is the background image of the City and County website.

And it’s difficult to limit access to a place that’s such a potent lure, for visitors and local residents alike.

But finding a way to keep down the crowds at Hanauma is precisely the challenge the city must work to meet in order to be the good steward that such a fragile ecosystem requires. Better enforcement of existing rules is needed and, above all, the city must get data to gauge the effect of this visitor load on the resources of the bay.

Taxis swarm into the Hanauma top-side parking lot daily: Cabs are allowed under the preserve rules, to allow for controlled visitor access. Each cab is supposed to have eight passengers but, as Honolulu Star-Advertiser writer Andrew Gomes reported on Sunday, tour companies find ways around such limits.

For the past 25 years the tour companies have dispatched buses that stop off-site and reload visitors into its tour vans that are registered as taxicabs.

Among the advocates seeking better management tools is Alan Hong, the longtime, now-retired manager of the preserve. Hong said drivers have been seen slapping the taxicab dome on the roof of the van shortly before entering the park.

The city doesn’t enforce the individual limits per cab, and these are generally not individual taxi operators bringing in private groups of passengers. Hong said companies often send larger groups by breaking them up into multiple vanloads of visitors.

The results: Crowds and long lines that discourage residents from enjoying the park — a consequence that the city vowed to avoid in its 1990 management plan.

The plan was developed in the 1980s to curb the environmental impact of heavy visitation levels. From the 384,000 annual visitors logged in 1975, the count skyrocketed to 3 million in 1988. It damaged the reef, fouled the water and put the fish population under stress.

Now, said advocate Lisa Bishop, the more typical yearly tally is about 800,000 visitors, which is within the park’s sustainability limits. However, Bishop, who is president of the nonprofit group Friends of Hanauma Bay, said a study is needed to determine whether even the lowered visitor count is continuing to harm the environment.

The city conducted a carrying-capacity study as part of its application for a conservation district use permit from the state Board of Land and Natural Resources. But, said Hong, one of the conditions of that permit was to continue the study to gauge the ongoing effects, but that has not been done.

The state should enforce its requirement and insist the city come up with the environmental measures needed to assess the impact. And then the city should re-evaluate whether it is doing enough to protect Hanauma Bay.

At the very least, the commercial vehicles should be charged a fee for accessing the park, whether it’s the buses that take groups for 15-minute stops at the scenic overlook, or the cabs that bring visitors for longer stays.

These funds will help with upkeep at the park, for residents, who pay no admission fee, to enjoy. That is the least that tour companies can contribute toward a destination that is generating a profit for them.

Bishop said Hanauma Bay could afford to admit fewer visitors annually and still stay in the black. If an entry fee increase is required, visitors likely would be willing to pay more.

But simply allowing the current indulgent enforcement policies to continue will effectively put a prized beach beyond the reach of local residents — and ultimately may lead to environmental damage. That’s a price Honolulu must not pay.