Hi Dragon fly larvae can be under water for up to 4 years depending on which breed

Ah thanks not sure if these black wriggerling things are Dragonflies they look like minature tadpoles, black there are lots of them

They sound like mosquito larvae to me. When the water is undisturbed and they don't know you're there do lots of them "hang" upside down from the surface? That's what mozzy larvae do.

No Beattie they have a strange way of swimming though. They kind of bring there front parts and their back parts together and move throught the water. Its really hard to describe