Tadpoles tend to be more prevalent at this time of year and, as they take about 12 weeks or so to become froglets, it's a good time to take some photographs.
A macro lens of 90 to 100mm is perfect, providing you have access to get close to the surface of the water. If not you will need a longer lens with a close focus facility. A tripod is handy to keep the camera steady as you take the photo, but you'll need one that has legs that splay out, such as Vanguard's Alta Pro 263AGH
, so you can get the camera closer to the pond's surface when using a macro lens. It's also better if the centre column swivels over 90-degrees to act as a macro arm so you can position the camera over the water's edge and not at an angle. It may be easier to lay down on the floor (use a waterproof sheet to keep you dry) and use your arms as support. A polarising filter will reduce any surface reflections allowing you to see more clearly under the water.
Tadpoles tend to be quite active, but move around in spurts. One minute they stop to presumably rest and then swim off to another spot. When they're active you need to hone in on one and follow it around, taking shots as it rests.
Look around the edges of the pond for the easiest shots. It's here where the tadpoles will be feeding off vegetation around the side of the pond, especially when they have no legs as they are not yet meat eaters. In the shot above the tadpole was slowly pecking away at the edge of the pond causing debris to burst back. This microscopic activity comes to life when a macro lens is at its extended range.
Use a fast shutter speed to prevent tail blur, and increase the ISO if you need a smaller aperture.
If the sun is out make sure you don't get the distracting rim where the water touches the side. This will appear as a white burnt out outline. Take the shots slightly away from the edge pointing inwards to conceal this outline. Shoot when the tadpoles are nearer to the surface to prevent the cloudy water making the image look dark.
Also watch for tadpoles taking in air - they swim quickly to the surface and gulp air in. At this point you can get a head on shot with mouth wide open, but you often have to be quick as it's a fast action.
When they tadpoles have legs they become carnivorous (meat eaters) so you can pop the odd worm, snail or piece of chicken in and watch them gather around in a feeding frenzie.