One off the interesting things about areas such as this has been how to mark them.
Back when I worked at the Northern CA GA I ran tournaments at the NLE Stevenson Ranch. There was a par 4 on the back 9 that had a pretty substantial carry over an area like this from the fairway to the green. In the winter it was a wetlands, but in the summer in the middle of the Central Valley it was bone dry.
The club marked it as a yellow water hazard (pre 2019 terminology). We were there when it was dry. If I left it as a water hazard, players couldn’t ground their club or removed loose impediments. Given I was running a Junior event, I didn’t want to trap a kid who might not have seen the stakes get penalized. Therefore, we pulled the stakes. If it had rained, players would get free relief for casual water. It was a dilemma.
But, fast forwarding to 2019 and the new Rules, I would leave it as a yellow penalty area. As of 2019, there is no penalty for grounding your club or removing loose impediments in a penalty area. If it did rain there wouldn’t be relief for temporary water.