This is a small section of the moat that runs north of the grounds of Jesus College in Cambridge. For months it has been covered in algae. But yesterday when we passed we saw that the wind had blown across the water from the east. This is as far as the wind had pushed the algae. And beneath the surface the water was clear, with leaves brown on the bottom.
The leaves must be from last year of course (it now being May) and they were in almost perfect condition, not rotted away. Perhaps the algae keeps the oxygen levels low and slows the decomposition?