When I bought the Aquatex glass for the main part of Lake Chiemsee, I asked for the pieces that were left over after they cut the blank according to the pattern I gave them. One of the extra pieces was rather large, so I shaped it a bit and used it as an extension that flows under rock walkway. (I was surprised as to how easy the Aquatex glass cuts!)
The lake extension also is a hatch, and I will post those pictures under the Layout Design forum in a day or so of how that worked out.
(NOTE: The thumbnails at the bottom of the thread are out of order; I had difficulty uploading the pictures last night.)
Thanks for looking!
Alex