How cold is the water they are coming from? I would start them out in that water.

Once in your live well you can cool the water with some ice. I would freeze your pond water perhaps. This way you can be adding it slowly as it melts. Not too much too fast as to shock them. You are just trying to cool the water not "chill" it. Remember you will have to warm them back up to your pond water. once home start adding your pond water to the live wells via water changes. You can simply add it and let it over flow as you go or remove some fist. once you get close to pure pond water and pond temps you can release them.

I like to do the final pond water exchange and release as early in the AM as Possible so the surface water will not be as hot.

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