Posted: 25/03/2012 at 18:46
Do you have ducks in the area? We have had a pair of Mallards visit early in the morning, they leave a dusty film on the surface of the pond. It clears after a shower but returns if the ducks do.
If the frogs laid their eggs a few weeks ago your spawn will be hatching. If there is no sign of tiny tadpoles and the spawn looks like it has been disturbed, look for newts, they eat tadpoles.