Walk back to the wooden beam you came from. Jump to grab the smaller one above the handhold you climbed up before. Pull up and turn having the entrance to your back. Jump to grab the next small beam which is above to the right.

Pull up and turn left to face the waterwheel.

Jump to grab the handhold ahead and traverse to the right. Jump to grab the next handhold on the right and, again, shimmy right.

Taking a detour for a Treasure - Let's go for a Treasure. Drop to the beam below and walk to the other side.

If you take a look at the opposite wall, you will see the Treasure inside the big pipe. Jump off the beam and use the Grapple to catch the metal ring above the pipe.

Climb down the cable line if necessary and angle Lara to the pipe. Swing and jump inside. Get the Treasure (8/28) and drop back into the pool.

Now make your way back to the handhold before dropping to the beam for the Treasure (as shown in the fourth image above).