Types of pollution include:

Fish waste

Aquatic turtle waste

Insufficient aeration

Dead leaves

Algae clogging hoses

Muck and leaves clogging an unreachable pump

Make sure your submersible pump is working properly so that your above ground filter can do its job. Backflushing the filter every day is generally a good idea, especially if you have a lot of fish (or large fish), while an aquatic turtle can really pollute a pond. If you have aquatic turtles, be sure to wear rubber gloves while cleaning to avoid salmonella contamination.

The easiest way to keep up with dead leaves is to be proactive. Minimize the amount of tree branches allowed to overhang the pond! Ponds need shade, especially in hot summers but willows and cottonwoods are especially bad since you will get both falling leaves and/or messy catkins and pollen for weeks at a time every year. 

Look online or at your local fish products store for long-handled nets. Adjustable-length handles are quite useful, but make sure you’re not using one that is really long. If you bring up muck or a thick layer of dead or dying leaves with a long-handled net, your back will really feel the increase in the weight of the muck that can cause you injury. Keep the weight you’re lifting as close to the body as possible.  It’s better to walk around to the far side of the pond than to reach across it. I’m not a medical expert but having a tricky back, I know from experience how much difference it makes.

Keep an eye out for algae. You will need to treat the pond on a regular basis, especially when you see spring algae bloom.  Even then, seemingly overnight, you can find sheets of green algae hanging in the pond water.  Fish will eat algae but they can be overwhelmed by it, too. Follow the instructions on the bottle, since each brand works a little differently, especially chemical versus biological control. Be sure to keep the pump and filter running because any algicide sucks oxygen out of the water.

If you don’t have long arms, try to keep your submersible pump as close to the bank as possible. You’ll appreciate that when you have to shut off the power to the pump and pull it out of the pond to clean no end of debris out of it, such as part of a plastic trash bag that has blown into the pond and been sucked into the pump.