Everything is deadly when it floods, with water floods being responsible for about half of all deaths from global natural disasters [0].

The Wikipedia article you linked to describes the event but says nothing about swimming through it. There's a Scientific American article that analyzed this based on the Reynolds number [1] and arrived at a conclusion that you can't swim through molasses via regular symmetric motions and would need something different, which sounds quite appropriate for the analogy.

[0] https://www.bmj.com/content/383/bmj.p2101

[1] https://www.scientificamerican.com/article/molasses-flood-ph...