Why did scientists add sulfuric acid to a Canadian lake for 17 years?

Scientists added sulfuric acid to Canada's Lake 223 every week from 1976 to 1993 to study the effects of acid rain. The experiment lowered the lake's pH from 6.8 to 5.2, affecting fish, invertebrates and the food chain. Although the water chemistry began recovering after the experiment ended, some ecological damage persisted for decades, with trout numbers remaining low.