BEIJING, July 18 (Reuters) - An outbreak of blue algae in a Chinese reservoir has left nearly 25,000 people without water and 100,000 others with reduced supplies, state media said on Wednesday of the latest in a series of water pollution scares.

The algae, in the northeastern city of Changchun, was likely caused by farm fertilisers and abnormally hot and dry weather, the official China Daily reported.

The local government had started collecting the algae using nets and boats and was trucking in water to residents in Changchun's Luyuan district where supplies have been suspended, the newspaper added. Other Changchun residents had had water pressure reduced, the Beijing Youth Daily said, showing pictures of fluorescent green-looking water in the reservoir.

Water supplies to millions of residents have been affected in a series of algae outbreaks across the country in recent months.

On July 4, water supplies to 200,000 people in Shuyang county, Jiangsu province, were halted for more than 40 hours after ammonia and nitrogen were found in a local river, state media reported.

In late May, a major outbreak in China's third biggest lake cut off water supplies to over 2 million residents of Wuxi city, also in Jiangsu.

Algae blooms develop in water that is rich in nutrients, often because of run-off from heavy fertiliser use, industrial runoff and untreated sewage -- all pollutants in ready supply in many parts of China.

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