Justin, about the waterfall, have you decided if you want it to come from the tank as in your last sketch, or from the sea as in lontalv's model?
In the first case it could be either spring water or sea water. Spring water could be natural, but sea water would have to be pumped, and one wonders why anyone would do that.
On the other hand it could be for powering something or for solving a puzzle. It reminds me of the way water is used on Serenia in Myst IV.
If it's sea water coming in because the ground is lower than sea level, then where is it going? It would have to be pumped up back into the ocean, or fall into some endless void, thus slowly draining the ocean.
Also, having salted or unsalted water will make a huge difference when you get to choose the terrain, texture and living creatures in the pond and the swamp.
With sea water, your pond could be a salt-water lagoon wich from my diving experience in Mexico can be quite beautiful and vibrant, with blue water, corals and colorful life.
Here are some pics I found on the net. Also think of places in Riven, like the village lake or the beach with the creatures sunning themselves.
http://g8.no/images/20060729084657_coral3.jpg
http://www.cruisewhitsundays.com/images/CoralLagoon.jpg
http://windom.cybox.com/photos/2005/02/ ... Lagoon.JPG
http://travels.edsventures.com/Philippi ... medium.jpg
http://coastal.er.usgs.gov/coral-microb ... ure2LG.jpg
http://www.gallerystthomas.com/images/a ... lagoon.jpg
http://www.coris.noaa.gov/about/what_ar ... on_186.jpg
http://www.wwf.org.ph/_userimgs/001-Cor ... als-13.jpg
With spring water, your pond could be a cozy, shaded place, still beautiful but less vibrant, with rounded rocks, moss, etc. Something like the pond in Eder Kemo with trees.