The secret level in which you destroy the reactor then collect the powerups has been quite a tradition in Descent 2 single-player level sets. Water Garden is the Obsidian equivalent of this type of level, with an added twist: You must find the hidden triggers to get any further. The more you find, the better the powerups get. At the very bottom, there are several Extra Lives, two Earthshakers and an Omega Cannon. There are several other powerups scattered throughout the level. It is suggested to enter this level with the Full Map from Pelorus. If you can find it, that is.
The basic objectives are to destroy the reactor and collect as many powerups as possible. Note that you will need to find hidden triggers to get any further. Some powerups are tricky to obtain.
There are two shakers, several extra lives and an Omega Cannon in this level. It's up to you to find them.