Females lay eggs as they are mating. Here the female (underneath the smaller male) is emitting a long string of black eggs. As they hit the water, the gel around them will swell, as you can see with the string of eggs on the upper left of the photo. The egg masses are quickly camouflaged as debris and bits of vegetation from the pond stick to the gel. This is a safety measure, hiding the eggs from predators.

Once the females have mated and laid eggs, they will leave the pond.