Hyrdophone in reeds at edge of pond

Two hydrophones lowered into the reeds near the shallow water at the edge of a pond to the north of the island. Occasional visible bubbles didn't appear to be registered by the hydrophone. What might be foliage being brushed by underwater currents and possibly the sounds of photosynthesis are audible. Every now and then, the seabirds in the sky above and a duck that has just landed can just be heard, their cries modulated by 50 cms of dark water. The heron that is 100 metres away keeps watch before launching into the air.