They don't look like ash. They may be pollarding the trees. Seems odd to cut them so neatly to that height and not just fell from the base
@helenczerski @leafster Yes I see what you mean. The thing is those cuts look clean and if planning to fell in stages the cuts would be left rough with the felling dips still in them. It would take an extra cut to leave them neat like that. Fingers crossed they are pollarded. If I can share your picture might be able to find out more as I am on an arboriculture forum.
@Beau @leafster They're surrounded by water, on a little mini peninsula. I don't think you could fell them from the base safely, and if you did they'd end up in the water.