[The architect's ] plan called for long straight alleys in patterns crisscrossing the park and, as the Emperor had asked, lakes and a long stream similar to the Serpentine in Hyde Park. Unfortunately, Varé bungled the assignment. He failed to take into account the difference in elevation between the beginning of the stream and the end; if his plan had been followed, the upper part of the stream would have been empty, and the lower portion flooded. When Haussmann saw the partially finished stream, he saw the problem immediately and had the elevations measured. He dismissed the unfortunate Varé and Hittorff, and designed the solution himself; an upper lake and a lower lake, divided by an elevated road, which serves as a dam; and a cascade which allows the water to flow between the lakes. This is the design still seen today.
And while there are many trees in the Bois, the one that caught my eye was the Redwood tree, the California state tree.
Hope you had fun doing this... I certainly did! (I also checked other maps of the Bois, confirming my find that this was the *artificial* stream that I'd run beside.)