awwwwwwwww memories lol it is dirty. the fine dirt will settle to the bottom of the pond also.
I need to do a little apology also, to you, sitting here trying to recall all we did, my husband reminded me.......... We did run the bog water out into the yard for a few hours instead of into the pond, for that first rush of dirt. Then we decided we would not worry about it and just filtered it out, we couldn't really drain the pond, easily, it took us a week to fill it due to our well. From your picture, i.e. size of pond, I would just say drain it a few times the amount of dirt will greatly decrease. Just run the amount of water your picture shows through the gravel then drain it.
Stir the gravel with a shovel, stick, piece of pvc, helps that dirt get out (careful of liner)
Love the amount of flow you have coming out, that looks so great, your rock work and all.