I sympathise. We have a drainage ditch on the other side of our boundary fence, so the ditch is on the neighbouring estate but they don't do any maintenance with it - our other neighbor reckons it's never been cleared out. It's half full of reeds, grasses, and in some places just plain old mud from the banks where the rabbits have burrowed.
Our field slopes down to the ditch but is slightly lower than the current water level just before it gets to the fence so it's not draining away. That part of the field is a bit of a frost pocket and having that much moisture down there really doesn't help. Actually, I need to ask a question about this in a separate post, but in the meantime I'll keep an eye on this in case there's more good advice on dealing with it.