> Covering a 4.2-mile (6.8 km) stretch of the Thames in West London, from Putney to Mortlake, it is over three times the distance of an Olympic race.

This is unbelievably challenging. The 2km race is infamous:

> Physiologists, in fact, have calculated that rowing a two-thousand meter race — the Olympic standard — takes the same physiological toll as playing two basketball games back-to-back. And it exacts that toll in about six minutes. [0]

Imagine doing that more than 3 times consecutively without stopping.

[0]: https://archive.nytimes.com/6thfloor.blogs.nytimes.com/2013/...

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