To be clear, I'm quite happy to sit on the bottom when the tide is out if the bottom is suitable, which is one of the main reasons I asked. Given the river, I'm expecting mainly mud. But, given the logging, there could be lots of undesirable stuff in the mud.
Yep. One of the first times I anchored with my brand new 35lb CQR right after I got Papillon, was in a bay like this that was used to store log booms. I did not know that and anchored in 15' and let out 100' of rode for a proper 7:1 scope on a windless night. That decision turned out to be double trouble. With no wind, I drifted all over the anchorage and my tracker in the morning showed that I had moved in progressively smaller circles with various centers.
When I went to pull up the anchor, I did not pull in more that about 10' before I came up tight with the line going straight down. Not willing to abandon nearly a $1000 dollars of gear, I spend the next 8-hours getting it back. What had happened was that the line had looped around numerous logs sticking up from the bottom. There were three of us on board and it took all of us to retrieve the anchor.
I brought the rode back to the ST 40 primary winch on port and then across the the starboard primary. Two of us would crank in with both ST 40s until the boat was heeled over about 15º. Then we would all stand on the port rail and at the count of three would jump across to the starboard rail which used the leverage of a 15,000 boat as a prybar to pull the log up an inch or two. Then we could get several more turns on the winch and do the jump again. after multiple lifts, the rode would finally slip off the end of the now upturned log and 5-10 of rode would come in with no effort until we got to the next one.
This was 25-years ago and the scars are still fresh. I think we had lasooed 5-6 logs. The worst part was the stench. Those logs had been rotting there on the bottom for years and as they came up, they sent out clouds of gas that would choke a horse.