Last monsoon, lawyer Saeed Ahmed and a group of 30 hired a houseboat to explore Tanguar Haor, or backwaters, in Sunamganj during the full moon of Ashar. The misty hills of Meghalaya, endless waters and tranquil greenery captivated him. But he returned to Sylhet with a rash that required medication. “I swam near the watchtower area, and soon after, I developed an itch that lasted two days,” he said. “Doctors said it was from the polluted water. The big boats dump plastics and all sorts of waste into the haor. I even saw them operating at night. If this continues, the haor’s beautiful environment will be destroyed.” For Saeed, the beauty was undeniable — but so was the need for...