The 6"-18" may be the ones we are most likely to see. When snorkeling last year I found them a lot at 2-3' deep. The shallow ones around the edge I could see from the bank. The deeper ones were not visible from the shore.
I made a spawning area that ranged from about one foot out to 4-5'. Put various size of small rocks and gravel in the area. A year later I took a backhoe and reached out as far as I could and deepened as much as I could reach because FA was horrible in the area. Now the spawning area that is left starts at about 2' deep or better. I found no evidence of BG use the first year when the FA was so bad, but the second year the BG kept the area relatively clean and there were solid beds as evidenced when I snorkeled.
One thing I would do different if I was doing it again. I would place some plastic tubs to put the gravel in to keep it from sinking into the mud so much. I like the looks of the concrete plastic mixing tubs sold at places like Home Depot. A person could either stack them edge to edge (they are rectangular) or space them out filled in between also with gravel.
They seem really durable and reasonably priced for the amount of plastic in them.
concrete mixing tubs The medium is the size/depth that looks good to me.
