I don't know much about reed beds, but last year I had ducks on my
pond and, as the
pond got smaller and their poop accumulated, I started to notice them getting wet feather and getting sick. I ended up having to
fence them out of the pond until the fall rains came and did a "water change" on the pond. They had access to fresh clean water, in both pails and trays, but they spent so much time in the pond that they still were getting sick. They got better once I fenced them out of the pond.
I would definitely keep an eye on them, especially looking for wet feather.