A small leaf moving in a seemingly random manner not following the flow of water caught my eye. Leaf porter crabs are known to grab on to small leaf-like objects and use them as cover whilst moving about scavenging for food on the bottom. The leaves protect the crabs from birds and also predatory fish.
The crabs grip the edges of the leaves with extra long arms and will wave their arms to turn over the leaves if they are 'overturned'. If they cannot manage to turn the leaf back, they will move to the underside instead.