River races are extremely popular among bucket-listers and people whom are weak swimmers because they assume there will always be a current to carry them along.
Newsflash: Rivers can be very stagnant and lack a current.
Rivers today are not like the rivers of two hundred years ago. Due to human intervention, we have changed the dynamics of how a river operates. Many major rivers have several dams in them to create lakes to serve as local reservoirs.
So with all these dams holding back the water, there is not a continuous flow any more. There won’t be any current unless the region has received a lot of rain recently. At that point the dams let water out, which will increase the flow rate.
To illustrate my point of how dams will rob a river of its current, just look at the Colorado River. For sixteen years, it did not reach its estuary because of human intervention. Basically that means we took so much water from the river it never reached the ocean. You can see how that is a bit of a problem. For more information on that story, see this National Geographic article.
As you can see, you should not be banking on there being a current just because it’s a river. Make sure you’re prepared to swim!