Clean-up efforts of the heavily polluted Danshui River in Taipei County have proven to be successful after researchers confirmed the return of 11 species of fish that were previously extinct in the river system, the Environmental Protection Administration (EPA) said Tuesday. Yang Hsi-nan, a researcher of the EPA's Environmental Analysis Laboratory, said the return of two species of goby and a species of cutler among the 11 returned fish species is an indication that toxin levels in the Danshui River have been greatly reduced. In the previous report dated 2002, only 27 types of previously extinct fish had reappeared compared with the current 38 species, he said. For example, he said, the monk goby was last seen in Taiwan over 20 years ago but because of the improved water quality, the fish can now be found along the Danshui River all the way up to the Xindian River, although the current population detected remains in the single digit range. 'Two or three decades ago, the government had loose regulations over the management of toxic discharge from factories. Much of the waste materials and chemical hazards from plants in Taipei County went directly into the river system,' he explained. Throughout the years, a score of politicians, including President Ma Ying-jeou, a former Taipei mayor, have listed cleaning up the Danshui River as an important platform, but none have ever produced the silver bullet to solve the problem. Yang said that although there has been a visible improvement in the water quality of the river, at this rate it will probably take about 40 years of clean-up work before the efforts are considered a complete success. One of the yardsticks of the effort, he said, will be the return of some benchmark species such as salmon. Similar to what is being done in the United States and Europe, Taiwanese aqua researchers have since 1993 been using a toxicity test to assess the level of acute hazardous waste in Taiwan's water, said Yang. The test involves putting different types of small organisms such as daphnia and brine shrimp into samples collected from water sources near factories to see how long the organisms survive, a test that usually takes four days. The researchers are also exploring another method of testing for chronic toxicity in the water such as antibiotics or endocrine- disrupting chemicals that cannot be detected by the acute toxicity test. The test period for this method is roughly around 28 days. Yang said the test method will most likely be officially announced next year and will be given to various agencies as an option for testing. 