Pteradon Pond
You can swim through the holes in the ground if bubbles come out of them.
I think the game is settling into a pattern. Glyphs, currents, glyphs, currents. And the occasional pterodactyl because we're in the Jurassic.
One glyph is half-obscured by the floor. I found it by using the map!
Another glyph both gives you the key and gives you the invincibility spell.
Near the end, there's one current that pushes you up through a long corridor into air. To swim down again, I had to do some flip trick--it seemed like I could only fight the current if I started by flipping Ecco from facing up to down.
And just a bit further, there's a current you can't swim through. You have to swim through a passage that looks like solid wall. This is right after talking to the glyph that asks why you're underwater if you breathe air. Good question!