NEWPORT BEACH, Calif. — An aqua-blue bay filled with white boats surrounds Balboa Island. In recent years, the bay has gushed over an aging sea wall when major storms strike at high tide. To alleviate impacts from projected sea-level rise in this exclusive enclave and other parts of Newport Beach, the city plans to spend $2 million in the short term, and potentially much more in coming years.

IMPERIAL BEACH, Calif. — With 1.5 miles of Pacific Ocean to the west, the federally protected Tijuana Estuary to the south and the San Diego Bay to the north, Imperial Beach, the southwesternmost city in the continental United States, is immediately vulnerable to the impacts of sea-level rise.

SOLANA BEACH, Calif. — As the ocean expands and rises because of climate change, coastal California homeowners are watching beaches disappear and seaside bluffs crumble, leading to controversy over whether sea walls built to safeguard their investments should be kept and added to.

DEL MAR, Calif. — Kim and Marilyn Fletcher stood on the deck of their beachfront home watching waves crash onto the shore. They savored the view from behind a 22-foot-high sea wall, a common sight along this eroding stretch of coast. But that view is changing: The sandy beach in front of homes in this north San Diego County town is shrinking, and the high tide is edging closer.

Unstoppable sea-level rise is coming to California's iconic coastline, threatening to transform beaches, boardwalks and oceanfront cities known worldwide. It's a slow but steady peril that state and local officials are just starting to address.