Coastal advocates are urging beachgoers to leave their fireworks at home — not only are they prohibited at the shore, they are a concern for sensitive bird species that live and nest along the coast.

Last Fourth of July,  a boater offshore from the Santa Ana River mouth appears to have scared off nesting California least terns by setting off fireworks from their vessel, Orange County Coastkeeper officials said. The endangered seabird species nests along the coast each summer.

“The Santa Ana River mouth is a critical breeding site for California least terns, western snowy plovers, and other shorebirds,” said Ray Hiemstra, associate director of policy and projects at Orange County Coastkeeper. “But these birds are incredibly vulnerable to human activity, especially loud noises, dogs off-leash and fireworks. Even well-meaning recreation can have devastating consequences.”

A few days after the holiday, surveyors confirmed that the colony was abandoned, “jeopardizing the immediate and long-term population growth of this species,” Coastkeeper officials said.

This year, there is a planned increase in the presence of government and nonprofit partners who will monitor the areas near the river mouth, which sits between Newport Beach and Huntington Beach, to protect the sensitive shorebirds.

Orange County Coastkeeper, OC Habitats, Huntington Beach Wetlands Conservancy, Sea and Sage Audubon Society and California State Parks will help with increased enforcement, public education and on-the-ground monitoring aimed at preventing similar disturbances and ensuring the protection of nesting birds.

While the boat incident put a spotlight on the area’s sensitive habitat, coastal advocates are also reminding people that fireworks are banned not just offshore, but also at Huntington State Beach, throughout all of Newport Beach, and along the coast of Huntington Beach.

Already, the holiday weekend draws the largest crowds of the year, with tens of thousands of people cramming into the coast from early-morning hours into the night.

While the least tern preserve is fenced off, other nesting areas for species such as the snowy plover are found around the sandy areas.

California least terns are listed as endangered at both the state and federal levels. Western snowy plovers are federally threatened and considered a “species of special concern” in California. Even brief human disturbance can cause them to flee, abandoning eggs or chicks in the process, according to Coastkeeper officials.

The area has been on the radar for environmentalists for years, concerned about the impacts of off-leash dog activity in the Santa Ana River mouth.

“This is about coexisting,” said Stacey Chartier-Grable, executive director at OC Habitats. “We all love our beaches. Taking small, respectful actions ensures that future generations of people and birds can continue to enjoy them.”

There are typically 300 nests in the area each season, though numbers in recent years have been dwindling, said State Parks Environmental Scientist Lana Nguyen.

Last year was the lowest number since 2008, with only 229 nests counted.

“This year, we’re looking at an even lower number,” she said. “We’re still hatching chicks and trying to fledge birds, but overall their numbers are on decline, and that’s consistent across California, it seems.”

Food supply is an issue, but disturbances are consistently a problem, Nguyen said. Around snowy plover nests, there will be temporary enclosures and fencing and volunteers standing guard, along with signage to warn the public about the sensitive habitat.

“We are entering a critical time, our visitations are busy and the Fourth of July is the busiest time of the year,” Nguyen said. “That many people on the beach usually means the plovers are hunkered down and can’t forage.”

The goal is to find the right balance between recreation and conservation.

“Give birds their space, respect fences and try to make sure activities are causing the least disturbance to both plowers and terns,” Nguyen urged, “so we can live harmoniously.”