How to write underwater on plaster

[fat-time]

Is there a good way to mark or highlight underwater cracks? I need to take photos for insurance purposes, and it can be hard to see them from the surface.

If possible, I'd like to trace the outline of the crack in something bright to help them show from the surface. Ideally, I can then wipe or clean the product up after.

My thoughts were:
- Chalk, but that might dissolve quickly underwater
- Crayons, but wax might be a pain
- [Hopefully] Some specialized product I'm not aware of!

Thanks!

 

[Pv2]

if on the floor, you could tie weights to bright colored survey tape and lay it along or around cracks

 

[Rocket J Squirrel]

Any reason not to take the photos and mark them up in photo editing software?

 

[fat-time]

Any reason not to take the photos and mark them up in photo editing software?

I can certainly do that as well. I'm having people out in-person as well and would like to outline cracks that are deeper on the walls and bottom. They're easy to see when in the pool, but harder from the surface.