Interesting chart from fivethirtyeight showing every event that's been in the Olympics since 1896

There was an open water swimming obstacle course in 1900:

Featured in 1900 (and 1900 alone) the combination swimming and obstacle event saw participants climb a pole, scramble over a pile of boats and then swim under a pair of boats en route to the finish line. All of this took place in the swift waters of Paris’ River Seine, adding an additional variable for competitors.

https://www.mensjournal.com/health-fitness/a-brief-history-of-obstacle-course-racing-and-the-olympics/

Would love to see tug of war make a come back, but is declared the only event where no drug testing is required.