Low thickets spill onto the sand from a number of oceanfront yards along the beach where Nancy Taylor has been walking for 35 years.

By law, every beach in Hawaii is public. However, Taylor and others say the beaches have narrowed drastically over the years, and it is increasingly difficult to distinguish public beach space and the yards of expensive beachfront homes.

"That's not public land anymore. I can't go there," she said during a recent afternoon stroll on Oahu's Kailua Beach, pointing to a verdant clump connected to the back yard of a private residence.

In recent years, some residents have complained that their neighbors are encouraging the growth of seaside vegetation to extend their properties closer to the shoreline, building a buffer between their verandahs and the prying eyes of beachgoers.

In Hawaii, where some vacant beachfront lots of less than a half-acre are priced as high as $7.5 million, making the most of every inch of paradise has become critical.

Public concern over decreasing beach space has prompted legislation, state-sponsored working groups and changes in how the state Department of Land and Natural Resources reviews the work of private surveyors. A lawsuit filed in July by the group Earthjustice on behalf of Public Access Shoreline Hawaii and the Sierra Club seeks to invalidate the state's definition of "shoreline."

Disputes over the reaches of beachfront property are not limited to Hawaii.

The California Coastal Commission has ordered residents of a section of Malibu to stop installing "Private Property, No Trespassing" signs along the beach and using heavy equipment to push sand from the public area up toward their homes.

The barriers, as high as eight feet in places, essentially shrink the public beaches in front of the homes.

Homeowners have said the barriers were meant to restore sand dunes that had washed away during storms -- not to block public access.

Property owners apply for shoreline certification in Hawaii when they decide to build. The location of the shoreline is first determined by a private surveyor hired by the homeowner.

Under state law, the shoreline is defined as "the upper reaches of the wash of the waves, usually evidenced by the edge of vegetation growth or by the upper limit of debris left by the wash of the waves."

However, department rules have refined the second part of the sentence to read: "usually evidenced by the edge of vegetation growth, or where there is no vegetation in the immediate vicinity, the upper limit of debris left by the wash of the waves."

Earthjustice and other critics say that language gives preference to vegetation, thus providing incentive for landowners to take over public beach land by planting more greenery.

"This is a loophole in the law that allows beaches to be only for those who own beachfront property," said state Rep. Brian Schatz (D), the co-sponsor of a bill this year that would have prohibited the practice of altering the vegetation line.

Since December 1988, only 19 of 2,896 shoreline certification applications have been appealed, with seven of those appeals coming in the past few years, said Peter Young, chairman of the Board of Land and Natural Resources.

"We're not talking about a lot," he said. "But we are talking about a very important thing."

Young said there is evidence of residents tinkering with natural vegetation lines, including installing irrigation systems that reach well beyond property lines. He said that he has asked a shoreline expert in his office to take a closer look at the sites that have attracted public concern, and that he hopes to add a second expert to assist in reviews.

Paul Schwind, director of research and legal affairs for the Land Use Research Foundation, which represents landowners and developers, said the best way to protect property owners' rights would be to come up with a more scientific system for certifying shorelines, such as one based on elevation.

"We're just trying to say, 'Let's quit arguing about things that may be difficult to do and don't really resolve the problem. Try something different, basically,' " he said.

Vegetation from a privately owned seaside property in Kailua Beach, Hawaii, slowly creeps into and diminishes an area accessible to the public.