Because he was holding the girls, Harry couldn’t use his hands to help propel himself through the water. He kicked his legs out as hard as he could, but after a short time they started to burn with muscle fatigue. Cho and the girl together were really heavy, and it felt like Harry was trying to lift sacks of stone. Around him the merpeople followed, rising up with him but keeping their distance. As the water grew lighter and easier to see, Harry started to feel the Gillyweed start to wear off. That meant he’d been in the lake for more than an hour, and that meant he’d lost. He found himself not really caring though, as long as Cho and the others were safe, that was all that mattered.