Lake Cook (directions here), also called Cook Lake, is little lake in Alexandria. It’s all of four acres, but is stocked in the winter with rainbow trout and has channel catfish. (You can check the Virginia government’s stocking schedule here.)
There’s a small parking lot next to it, and Cameron Run —which is fishable— is across the street. All of which makes Cook Lake and easy-to-fish experience. I’ve hauled three young kids there without any trouble. All of them caught trout.
The lake appears to get perhaps 15 foot deep. Trout, loving cool dark waters, tend to hole up in the middle of the lake. Conveniently, there are two fishing platforms that enable long casts to the lake’s center. That said, trout can be found all over the lake (after a stocking), and you can wander anywhere about Lake Cook’s perimeter and cast with ease.