Field notes: A New Zealand stream

At the edge of a clear stream, sunlight reaches the water and helps algae grow on rocks. Mayfly nymphs graze on the algae. Small fish eat the nymphs, and a kingfisher catches small fish. Fallen leaves from nearby mānuka and kānuka trees enter the stream. Fungi and tiny bacteria break down dead leaves and animals, returning nutrients to the soil and water. The stream also contains water, rocks, air and sunlight. After heavy rain, the water becomes faster and cloudier.