How do clams get where they are?

Question

About three years ago we dug a pond out in a peice of our property. We stocked it various fish. Now its full of clams. How did they get into the pond? This is driving me crazy :)

Answer 1

When you say 'clams' I assume you are referring to a freshwater variety of mollusc?  When you stocked your pond with fish and aquatic plants (macrophytes), juveniles or larvae may have been attached to the macrophytes.  It would only take a couple to grow to maturity to start populating your pond!  

Answer 2

Darwin did an experiment in which he held ducks' feet in water containing the larval stages of various organisms to see if the larvae could survive while the bird flew to another body of water.  His studies were among the first to confirm that larval stages of aquatic organisms could survive in mud on the feet and feathers of ducks and wading birds.  So a migrating duck or wading birds could have inadvertently brought the clams to your pond.

Another possibility is the larval stage of the clams could have been in the water from the fish hatchery's ponds.  It would only take a few to populate a good habitat.

Answer 3

Clams as larva can be carried around by fish and other marine animals.   Of course they drift with the currents and can swim a bit. They can also hitchhike over significant stretches of land on the feet of birds.

On their own, and grown up, some clams are very  good at burrowing (These burrows with clams in them are fascinating fossils when collected correctly), down or sideways.  Some clams swim by opening and closing their shells quickly.  And some can jet, pushing water out through a tube used for intake and "outake" of water