Seawater is causing problems for two million people in Shanghai. The city is enduring its longest-lasting salt tide in more than 20 years. As of this morning, the salt tide intrusion has already lasted for 21 days, the longest since 1993. Shanghai is located at the mouth of the Yangtze River.

The intrusion occurs periodically, especially in winter and spring when the Yangtze water level is relatively low. High salt levels in water is harmful to people's health, machinery, and crops.

Shanghai's water authorities say the reservoir built in 1993 can only hold a ten-day water supply. They have established a comprehensive plan to coordinate the city's waterworks and appealed to the national government for support.

Chen Guoguang, senior engineer of Water Supply Distribution & Monitoring Center, said, "Together with the previous two salt tides, the intrusion this time is causing huge harm to our water safety. The whole process isn't expected to end until early next month."