Beijing and Hebei Province strive to protect water sources with a planting project that has seen 600,000 mu (40,000 hectares) of trees grown along the two neighbors' major river courses and reservoirs over the past five years, authorities said Monday.

More than 50 million trees have already been planted, mainly along the major river courses in Zhangjiakou and Chengde, two cities in Hebei, which are the shelter belts that protect Beijing from sandstorms and are major water sources for the region.

Forests, grasslands and wetlands are nature's water filters.

According to the Beijing Municipal Bureau of Landscape and Forestry, another 100,000 mu of trees will be planted in these regions in 2016. Beijing and Hebei will plant a total of 1 million mu of trees to protect water sources by 2019.

Thanks to the tree-planting project, forest coverage in these regions was 41.7 percent in 2014, increasing from 37.7 percent in 2009 when the project began.

Northern regions are facing severe water shortages. A south-to-north water diversion project, which has redirected water from a tributary of the Yangtze River to Beijing since 2014, will go some way to addressing this.