Improvements to the marine environment are likely to have led to the return of white dolphins to Shenzhen Harbour in China's Guangdong province after more than a decade's absence. In the past few weeks, officials with the Nanshan Supervision Station of the Shenzhen Maritime Safety Administration (SMSA) have sighted five-six white dolphins chasing each other playfully almost every day in Ciwan Bay in the west of the harbour. SMSA official Li Ying told China Daily : "It was not rare to see this kind of valuable animal, which is under the country's first-grade protection, in the 1980s in this area. But with the seawater there continuously degraded, we have found none of them in the past decade,' said Li Ting. Shenzhen Harbour became the country's second largest container port in 1998. Its economic rise took less than 10 years. However, one byproduct of the rapid economic development was the deterioration of the local marine environment.