Adding a pond to a stream - any guidance?

Rather than interfere with the stream would you not dig the pond on the field side and have a pipe flowing into it.

My worry in widening the stream to form the pond that the water would just flow through it and not be still water which is what you need for a pond.

First dig a temporary trench around site of pond to keep clean water flowing while digging out pond ( farmers downstream may have cattle drinking from stream ) Get digger driver to dig pond a little deeper than finished level (removing any large stones etc) then put back a layer of clay/topsoil and smear/compact it with back of digger bucket to seal (might have to wet it slightly). If the stream flows year round sealing won't be that important anyway (stay away from plastic/rubber liners) Finally a small "island" feature at widest point is a great feature to include if you can. Best of luck, looks like ideal spot for one

The problem with that is the water in the pond will become stagnant ( all the fresh water will just flow in the stream once the pond is full )

A lot of pond videos on youtube are american but there is an irish one called Heather Hill Farm who put in a pond recently with some good advice

Just assumed I suppose, mine are fed from springs so fresh water coming always. See some US farming videos and they have to put in aerators to blow air in to keep water fresh for cattle. I know you can add certain plants to do the same job. Would evaporation be enough in a larger pond?

A lot of those US ones appear to be reservoirs and they do stagnate. So by putting fish and plants in to balance the algae growth you then necessitate aeration. But it's a tricky one to keep a balance on as the water temps can rise massively, algae can explode and the pond can crash rapidly, so you need shade and depth and weed management and a well established environment.

Anyway, a pond of that size fed by a stream with through-flow wouldn't stagnate unless it was badly laid-out and had muddy shallows. If the sides are kept steep enough, roughly greater than 35 degrees, it should all work together. Having natural rounded stone would be beneficial to create an rocky in-flow delta at the water-line, that's where many of the insects will hang out and around as well as the birds, etc. Think about depth - if there are likely to be kids in the area then it all needs to be kept relatively shallow. Add a shingle beach area (2m sq) for access. As long as the livestock is kept out of it, it should flourish.

Give the digger-man the layout but first work out whether you need lining clay brought in or not. Take out and retain any existing stone and retain it, then dig and line it in a day and return the stone to make the features. Sounds easy from here. 😆

😂That's the funniest thing I've read on here in a while