A couple of weekends ago I was having a walk around Sand Hutton Gravel Pits, a gin clear gravel pit near us here in York. This is a wildlife heaven, perfect for anglers, dog walkers and bird watchers alike. The pits in Sand Hutton date back to the Triassic years, and underneath them is mudstone.

It struck me how crystal clear the water was. Throughout the winter we still get customers who have green water and blanketweed in their ponds, so what’s the key to clarity of water?

Filtration – If you have high fish stocks, this is the only way of achieving a gin clear pond. By working out the volume of water in a pond (L x W x D x 1000 Metric will achieve the volume of a square) we can pretty accurately (with the help of supplier’s guidelines) work out which filter and pump will give you crystal clear water.

Plants – Plants use the same nutrients from your pond water as algae and blanketweed do (the ones that come from fish waste, rotting matter etc). So in theory the more plants you have, the better the water quality will be, as these nutrients will feed the plants and you won’t have much left over for algae and blanketweed to feed and grow from.

Reducing Sunlight – Shade over the surface of a pond will help to create a clearer pond, as we know, the less sunlight, the less algae can photosynthesise.

So, what do Swan Mussels have to do with any of this? Well back to my original paragraph, when I was walking around the gravel pit, I found the most enormous swan mussel shells on the bank side (I am assuming these have made a tasty snack for some predator), could these be the reason for the gin clear water?

They certainly won’t be a hindrance, these mussels at full maturity will reach sizes of up to 6 inches, filtering up to 40L of water a day. Feeding on single cell algae and daphnia they are perfect for larger mature ponds and can live for up to 12 years. There are actually five different types of fresh water mussel that live in lowland rivers on British shores, and one which lives in upland rivers which is the pearl mussel. Mussels are in fact pretty common, in clear streams you’re pretty likely to see them, so take a careful look out for these guys when you’re walking through these crystal clear streams in the summer!