Is this a Parasite or Pond Worm Leech?

[Goldfishpond]

Does anyone know what this is. I found inside my Pond Thermometer next to my Potted Plant. Looks like a leach but stretches to a flat worm. Is it a tiny flatworm or leech what is it? Is this a parasite dangerous to my fish?
It’s teeny tiny but 2nd to last picture is closeup before it wiggles when I took thermometer out of water it stretches out and moves like a worm or leech.

 

[j.w]

@Goldfishpond
I'm guessing flatworm.

 

[GBBUDD]

Parasites generally are to small to see with the nakedness eye. Ick being an exception.

 

[Goldfishpond]

Thank you for information

 

[rwood]

Fish would keep them under control