The governments of Xi'an and Xianyang, two major cities in northwest China's Shaanxi Province, have been fined a total of 500,000 yuan (73,530 U.S. dollars) for polluting a tributary of the Yellow River, China's second longest waterway, the local environment watchdog said Thursday.

The two cities are the first to be penalized by the provincial environmental protection department since new measures to curb water pollution took effect on Jan. 1, said Li Xiaolian, deputy chief of the department.

According to the new measures, city governments will be fined for excessive discharges that cause a rise in "chemical oxygen demand" (COD) -- a measure of the amount of oxygen consumed in the chemical reactions in water as a result of pollution.

The penalty is 100,000 yuan for every milligram per liter of excessive COD in the local river water, Li said.

In the latest water quality check last month along the Weihe River, a major Yellow River tributary, the Xi'an section was found to surpass the upper COD limit by 4 mg per liter, he said.

The Xianyang section on the upper reaches topped the limit by 1 mg.

"The penalty is not a huge amount for the two cities, which rank as the first and third biggest economies in Shaanxi. But it's a loss of face for the local government and will prompt them to do a better job," said Li.

The fine will enter a special account of the provincial treasury. About 60 percent of the total will be appropriated to local governments at the end of the year as an environment preservation fund.

An environment official in Xi'an, however, complained it was "unfair."

"Xi'an is a big city with nearly 10 million people. It also contributes nearly 50 percent of the provincial GDP," he said on condition of anonymity. "The pressure on us is therefore much higher than other cities."

The official also complained about the monitoring results, saying the COD and density of pollutants would be higher in the dry season. "It's not fair to apply just one standard everywhere and throughout the year."

The provincial environment protection department published the results of water quality checks every month. The monthly average COD measure was calculated on the basis of the daily data, collected once every four hours, Li said.

The Weihe River, which runs 818 kilometers, also flows through Baoji and Weinan cities. It was seriously polluted over the past two decades, as a result of waste discharges from hundreds of paper mills and other highly polluting plants.

"In the worst days in 2005, its water turned dark and stinky, with white foam on its surface," said Zhang Runmin, an environment official in charge of water quality along the Weihe River.

Since then, the province has shut down more than 700 paper mills and stopped approving new polluting projects along the river.

The province has set up 62 sewage treatment plants to minimize pollution to the river.