Two Chinese men have been arrested for allegedly discharging hazardous acid waste into the Grand Canal, a World Heritage site, said local procurators.

The suspects were accused of releasing toxic waste into the Suzhou section of the canal, the world's oldest and longest artificial waterway, since October 2013, said the procuratorate of the Wuzhong district of Suzhou, Jiangsu Province.

The two used waste acid to produce a water-purifying agent and then deliberately allowed the used material, stored in a leaky container, to enter the waterway.

Local authorities ordered them to stop production of the agent in 2013. The suspects continued to collect waste acid from other factories, which paid them 120 to 150 yuan ($24) per ton to dispose of the waste.

As of February, they received around 90,000 yuan from factories and simply let the waste leak into the canal. Their trick was discovered by local police last year after data showed abnormal fluctuations of water quality in the canal.

In June 2014, UNESCO included the Grand Canal in the World Heritage list. The 1,011-kilometer waterway is the largest civil engineering project before the Industrial Revolution.