The fishpond's wall encloses an area of 88 acres in the southern reaches of Kaneohe Bay on Oahu's windward coast. About a quarter of its perimeter is bounded by the bluffs of the shoreline, where private homes now sit. The rest is open wall rising from the bay floor, constructed entirely of dry-stacked basalt and coral stone. The design is deceptively simple: two gates, called makaha, allow water to flow in and out with the tides. When both gates are closed, any marine life too large to slip through the openings is trapped inside. Fish grow in the protected, nutrient-rich waters, and harvesting becomes a matter of wading in and collecting what the pond has raised. The system also supports crab, shrimp, and eel, a complete protein supply engineered from stone and tide.

In 1965, a flood destroyed over 200 feet of the fishpond's wall. The damage was severe, but what followed was worse: decades of neglect during which invasive mangroves colonized the broken sections. Mangrove roots are powerful enough to pry apart stonework from the inside, and their dense growth choked off water circulation within the pond. By the time conservation efforts began, the damage ranged from a few missing stones at the top of the wall in some sections to total collapse down to the foundation stones, called niho, in others. The fishpond was rezoned as conservation land in 1974, a designation that protected it legally but did nothing to repair the physical structure.

In 2003, the nonprofit organization Paepae o He'eia became the fishpond's official steward. The restoration work is deliberate and labor-intensive, guided by the same principles that built the pond centuries ago. Volunteers and staff rebuild the wall by hand, fitting stones without mortar, clearing mangroves, and removing invasive species. Bioretention basins have been installed to filter pollutants from storm drain runoff before it enters the pond, addressing a modern problem that the original builders never anticipated. The University of Hawaii has contributed research and assistance, and the fishpond now serves as a living laboratory for marine science alongside its cultural and educational mission.

He'eia Fishpond is more than an archaeological artifact. It is a working demonstration of sustainable aquaculture, a system that fed communities for centuries without depleting the bay's resources. The kuapa wall creates a controlled environment where brackish water, a mixture of fresh water the Hawaiians called wai and salt water they called kai, supports species adapted to that specific salinity. The fishpond concept itself reflects a deep understanding of marine ecology: by managing water flow and enclosing nursery habitat, Hawaiian engineers created a renewable food source that could be harvested without overfishing the open ocean. In an era of industrial fish farming and collapsing wild fisheries, the 800-year-old design at He'eia still has something to teach.