Marine officials are blaming cross-border oil spills for an unusual increase in contamination of beaches and coastal areas last year. They say shipping activities, including ship-to-ship oil transfers and illegal discharge of bilge water, possibly outside Hong Kong waters, were at least partly responsible for the spills that have been getting worse, affecting such areas as Lantau, Lamma and the south of Hong Kong Island. Of 66 spills handled after receiving a five-year high of 168 complaints, the Marine Department could trace the source of only 15. 'Those whose sources could not be identified are suspected of coming from vessels discharging engine bilges at night, or waste oil poured down storm drains,' a department spokesman said. Most spills were minor involving rainbow-coloured oil film or darker diesel oil affecting an area no greater than 1,000 square metres and involving only about 10 litres of oil, the department said. The department blamed oil from vessels passing through or near the Dangan Channel between Hong Kong's southern marine boundary and Dangan Island, administered by Zhuhai and known as a hotspot for leisure fishing and scuba diving training. The channel connects with the East Lamma Channel through which up to 400 ships including ocean- going vessels reach Hong Kong's inner harbour or Kwai Chung container terminal every day. The area is also reported to be a key smuggling route for oil, vehicle parts, electronic components and even wild animals between Hong Kong and the mainland. Hong Kong Fishermen Consortium and Southern District councillor Dr Cheung Siu-keung said oil spills in southern waters could be related oil barges illegally supplying fuel to vessels in areas not designated by the Marine Department. 'The barges are said to be covertly operating at flexible locations near the border, making it difficult for the police and marine officers to spot and chase them,' he said. Hong Kong Shipowners Association managing director Arthur Bowring said it was unlikely for oceangoing vessels to refuel or discharge bilge content at sea as they were subject to stringent international rules and record-keeping requirements. 'Bilge oil in Hong Kong waters is far more likely to come from local or river trade ships, fishing boats, or private junks which rarely travel outside the Pearl River Delta and Hong Kong waters,' he said. Bowring said oil, as with rubbish, might sometimes be washed from shore to sea by rain or through illegal connections to the drainage system. Marine officials said they would liaise with Guangdong officials over control measures in the Dangan area while the Government Flying Services and Marine Police would also step up patrols in the area. Inspections of oil barges anchored in southern waters would be boosted to ensure their pollution prevention measures satisfied licensing conditions. Of the 15 oil spills that were sourced to their location last year, seven resulted from breaches of the law. Twelve summonses were issued, leading to 10 successful prosecutions and total fines of HK$33,800. The 66 oil spills also led to beach closures on 49 days but no figures were available on the clean-up cost. In Southern District, seven spills were recorded last year, compared to one in each of 2008 and 2009. In July last year, Repulse Bay beach was closed for two days because of an oil slick from an unidentified source. The latest contamination was in mid-June, when oil patches covering 900 square metres were found at Deep Water Bay. Samantha Lee Mei-wah, a senior marine conservation officer from WWF Hong Kong, said the ecological impact of such spills would depend on the location and scale but they could also cause nasty experiences for swimmers. 'I visited Big Wave Bay recently and it was nice to swim in the pristine water. But when I left the water I found something stuck to the bottom of my foot. The small patch was dark brown in colour and a bit thick,' she said. 'I tried to clean it with soap but could not even after repeatedly trying. It could be only be rubbed away with strong kitchen detergent.'