Identifying barrier between floorboards and ply subfloor

[longbloke23]

Hi. I'm prepping our bathroom for new flooring and some minor plumbing (moving waste to below floorboards) so have lifted ply to get a look at floorboards and found this layer. Looks like a combination of adhesive and material, stuck onto floorboards, comes up in pieces with a scraper but not easily or neatly.
Can anyone tell me what it is, whether there's asbestos risk, and if not, then tips for removing?
Thanks!

 

[Elkato531]

Pretty sure its not asbestos. Looks like some sort of underlay of floor backing. If you're worried, wet it thoroughly so there is no dust but its going to be a case of going at it with a scraper.