Does your pond smell a little worse than a basket full of rotten eggs? Do your nostrils become melancholy each time you venture into your backyard? Have your children and pets stopped going near the pond? Well, it’s time to do something about that bad smell. Why Ponds Stink Ponds stink when they are not aerated. The lack of movement in the water causes stagnation, which in turn makes the layers of water in the pond acquire different temperatures, a phenomenon known as stratification. While the layers at the top always receive some oxygen from the surface of the water, the bottom layers become locked away for weeks, even months, during which they become entirely depleted of oxygen. Anaerobic bacteria form at the bottom, and they digest the sludge and produce bad-smelling waste products. The bad smell will stay at the bottom of the pond so long as the temperature remains constant. But when shifts in the temperature occur – and they also do when the seasons change – the bad smell rises to the surface. If you have a sensible nose you’ll smell the invisible rotten eggs in no time. If not, the expletives of the neighbors will make it clear that something is wrong with your pond. But the worst part is not the smell. As you can imagine, the stale water that rises to the surface is full of bad bacterias and murk. It’s unwealthy for the fish. And it won’t look good either. A complete clean-up is recommended. Move the fish, pump out the water, vacuum-clean the bottom, add in fresh water with beneficial bacteria, and then refill the pond and add the fish. It’s better to prevent the problem than to have to solve it though. And the solution is quite simple: install a water aerator. If you have one already, it’s clearly not sufficient, and you want to replace it with a newer, more powerful model, and possibly also add water features such as fountains and waterfalls that keep the water moving. Use More Diffusers A good tip is to look for a water aerator that has two or more diffusers, especially if your pond has an irregular shape. Conventional diffusers lay on the bottom of the pond and aerate from the bottom up, ensuring that the lower layers of water are always aerated. Beware of surface diffusers that rely on gravitation to aerate the pond. If they are not strong enough, their aeration will not reach the bottom. Don’t Forget to Clean In rare cases, bad pond smells are not the result of lack of aeration, but of outstandingly poor maintenance; the pond is so full of decaying leaves and twigs and rotten fruits and dead fish and weeds that they cannot help but stink. A throughout cleanup is recommended, as well as a drastic change in the pond keeper’s habits. Finally, you will also want to ensure that your filters are doing their job. If they are dirty, clean them. If they are old, replace them.