Gecques Courstau is the underwater level in Gex 64: Enter the Gecko. It is exclusive to the Nintendo 64, with the other platforms receiving Poltergex instead.
For the water level, the control stick will turn Gex around, 
will swim forward, 
does a spinning attack, and 
will stop movement.
Swim Through Three Arches[edit]
All three arches are in the initial chamber. Two are against the wall, while one is in the middle.
When you swim through all three arches, the red remote becomes available.
Find The End Of The Cave[edit]
For this red remote, you can get the silver remote on the way. You can also attempt to collect the 120 pickups for the other silver remote, although this isn't the ideal scenario.
In the first chamber, look for the turtle taxi, found near a sunken motor boat and marked by a sign. Riding it will bring you to a second chamber. Look for another turtle taxi, likewise marked by a sign. This leads to the cave you need to explore.
The cave will have groups of jelly fish rise from the floor at certain points. Let them pass, then swim through.
The other paths contain things you may be interested in. If you're simply heading to the red remote, take the left tunnel at the first branch, right at the second, and left at the third. At the cluster of collectables, turn left, and you should see the red remote.
Reach The Top Of The Titanic[edit]
If you don't have the silver remote for collectables, this is probably the best choice to pick. Simply explore the caverns as much as possible.
To reach the Titanic, head to the water's surface in the first clearing. You should see an iceberg, and can enter the Titanic by entering the titanic tours sign.
When you enter the titanic, flip the switch behind you to power the bulkhead doors. Flip the switch near each door to either open or close it, but note that only one door may be open at a time. Before opening the next door, flip the switch near the previous door before flipping the switch for the next one.
The final bulkhead door is harder to pass through, as you have to go through while it is raising or descending.
In the main hall, ascend the stairs, and circle around the second floor. You will want to avoid the water if possible, as it either pushes you or causes you to slide down. Jump across the flowing water on the second floor, and enter the small window.
Outdoor ascent[edit]
On the outside of the titanic, you will need to use the tailbounce to jump onto the various stacks and features. Note that falling into the water will cost a life, rather than returning you to earlier
On the first platform, tailbounce using the black knobs onto the center white building. Then, tailbounce onto the smoke stacks to reach the upper middle one. This will transport you to the upper section.
Head left, and jump onto the mast, and slowly walk towards the camera. Once you can freely ump upward, land on the platform above. Tailbounce over the last remaining structures to reach the red remote.
Silver Remote[edit]
Head to the cave, similar to what was donw in the silver remote. Take the left, right, and left branches as normal. Instead of taking the final turn to the red remote, instead head straight, and upward. This brings you to a fourth opening, and the silver remote is found at the water's surface.