If you look at a block while under the water, then under the 'Targeted Blocks' section it will appear despite the fact there is also a 'Targeted Fluids' section and the 'Targeted Blocks' section should say whatever non-fluid block I am looking at.
is duplicated by
MC-130586F3 menu shows minecraft:water and minecraft:lava in both "Targeted Block" and "Targeted Fluid" categories
MC-131035Targeted Block shows mincraft:water when looking at underwater blocks
MC-131362While under the sea, the F3 menus's "Targeted Block" line displays water despite other block is targeted