Question
CAN I GET RID OF THEM

Answer
I assume your swimming pond also has animals in it that you don't want to harm?  Have you seen these leeches attached to people or animals?  If not, there are leeches that eat detritus that are naturally found in ponds that are harmless.  If you have the ones that eat blood, you can catch many of them but hanging a piece of meat like liver in the pond over night.  By morning, it should be covered in leeches that you can remove.  There are no chemicals that will kill leeches that won't also kill other animals.  Dimilin at the right dose won't kill fish but will kill leeches and many other invertebrates.

http://www.koi.com.my/forum/KOI_Talk_C1/Pond_Water_Quality_F3/leeches!!_P6390

http://www.thatpetplace.com/pet/prod/199632/product.web

Good luck!