So, there is field horsetail, marsh horsetail and water horsetail (Equisetum fluviatile), I guess it is not difficult to work out which one you are most likely to find in ponds, lakes and slow moving rivers! Water horsetail is common in the muddy margins of fresh and in such suitable habitat there can be lots and lots of it. It has been designated an obnoxious weed in some places as it can be virtually impossible to get rid of once established.
Water horsetail is bright green all over with dark scales around the 'branch' joints and it is a tall, slender plant compared to some of the other horsetails. The stem is hollow and will collapse under very little pressure from a couple of fingers sqeezing it.
As with other species of horsetails it is adept at absorbing metals from the soil and is used for analysis and extraction of these substances. It also has some long standing medicinal properties but different parts of the world consider it to be cures for differeing ailments so I suspect none of these are really well founded. Horses refuse to eat it (why would they eat their own tails? [joke]) but reindeer apparently love it as it is so juicy. One animal's meat is another's poison I suppose!