In the 1920s, when the Republic of China government was consumed by the Northern Expedition — the military campaign to reunify a fractured nation — the bay became what ungoverned coastal waters often become: a refuge for those operating outside the law. Piracy flourished in Bias Bay, as Western sources of the era called it, and the bay's reputation for lawlessness reached international shipping circles. British and other colonial-era newspapers carried warnings about vessels attacked in these waters. The Canton Operation of the Second World War brought a different kind of intrusion: Japanese military forces seized part of the bay as part of their campaign to take Guangzhou. These layered histories — piracy, colonial anxiety, wartime occupation — are largely invisible today, submerged beneath the bay's modern identity as an energy coast.

Before the 20th century reshaped the bay's ecology, Daya Bay was a significant site for marine mammals. The Western Pacific population of gray whales — now one of the most critically endangered whale populations in the world — used the bay as a calving ground, migrating here in winter and spring to give birth in its protected waters. Humpback whales also visited historically. Japanese whaling operations, which established stations at multiple sites along the Chinese coast, wiped out these populations from the bay. Today, they are gone. What remains is a partial, painful recovery: critically endangered Chinese white dolphins have been confirmed in Daya Bay in recent years, and occasional humpback sightings have been recorded. The bay's marine life is fragile and closely watched by researchers who know how much was lost.

Daya Bay's modern identity is shaped, above almost everything else, by the Guangdong Daya Bay Nuclear Power Plant — the first large-scale commercial nuclear power station in mainland China, which began operations in the 1990s in a joint venture with Hong Kong. The plant's reactor domes and cooling towers are the most prominent features on the bay's western shore, drawing water from the same bay that once sheltered gray whales and pirates. The nearby Ling Ao Nuclear Power Plant expanded the complex further. Together, these facilities made Daya Bay an energy corridor of national importance. They also made it the perfect host for something unexpected: particle physics. The reactors produce such vast quantities of antineutrinos that they became the ideal source for the Daya Bay Reactor Neutrino Experiment — an underground detection project that achieved a landmark measurement of neutrino oscillation.

The bay connects to the broader Chinese rail and road network through the freight-only Huizhou-Dayawan railway, which carries cargo rather than passengers. A planned Shenzhen-Dayawan intercity railway would eventually bring faster passenger connections to this corner of Guangdong, linking the bay's shores more directly to Shenzhen's transit network. The Dapeng Peninsula forms a natural western barrier, its mountains and beaches shielding the bay from the most intense development pressures of the Shenzhen metropolitan area. To the north and east, Huizhou's jurisdiction shapes a landscape that is more industrial and less touristed than the peninsula. The bay itself remains contested terrain — a place of significant ecological value, continuing industrial development, and scientific investigation happening simultaneously, sometimes uneasily, on the same stretch of South China coast.