BBC News today has an item suggesting the the freezing over of ponds is actually good for them, contrary to apparent logic.
I see the basic logic behind the article, emphasising that freezing over could increase the oxygen levels in the water, although I would like to see some evidence of this being true. However as a long-time pond keeper (aka. fish keeper) and as the moderator of an online aquatics forum, I would not agree with a number of the ideeas and suggestons made in the article which I think are potentially misleading (or worse) ...
Received wisdom says that pond owners should break a hole in the ice to allow oxygen to reach the water.
NO! Never break a hole in the ice. They get it right later: "make a hole". Do this either by keeping an area clear (eg. with a football or a pond heater) or by melting a hole with hot water. Never, never smash the ice if there are fish in the pond: the shock wave will likely kill the fish.
Making a hole in the ice makes very little difference to the amount of oxygen in this water
This is probably true, but a hole could make a difference if there is a concentration of other unwanted gasses in the pond water.
The only time that pond owners should intervene is if they own fish, or the bottom of their ponds are full of silt and dead leaves. Then it is worth stirring up the water
Again I would disagree. If you have fish, do NOT stir up the water. The water may be layered into thermoclines with slightly warmer water at the bottom which will benefit the fish. Moreover if you have fish and a silty bottom (!!) then disturbing the debris can release potentially toxic gasses like ammonia – it may also disturb hibernating amphibians. If you're going to stir up the bottom of your pond to remove detritus, then do it in mid-summer.