Paddling upstream in South America

We are a couple who wants to paddle upstream a river in South America, we would like to ask a few questions:

What kind of paddle is better for a tandem canoe upstream with long journey - one blade or double blade?

How far and fast can we expect to move, since we will be loaded with equipment and food.

I assume that the further upstream the stronger the current, and that the tributes are much weaker and slower than the main river. Am I correct? I’ll be happy to get more information about this subject.

Any advice, tips, knowledge (personal or books) and help will be highly appreciate,
Thank you.

Sounds like an interesting trip!
For long distance canoe paddling single blade is generally considered better.
As for speed, your speed will be your flatwater speed minus the current speed, plus a little speed you can pick up here and there by riding eddies. If you don’t know your all day flatwater speed you probably should do enough paddling to know that before planning the details of an upstream river expedition. All day flatwater speeds will vary wildly with paddler fitness and canoe choice, so it is impossible to make any useful generalization.

If there are any outfitters along the stretch of river that you plan on paddling, they would be the people to ask, as well as any local tourist agencies.

A heavily loaded canoe will be much slower and more affected by current, but less by wind. You would have to experiment.

Be aware of flood or drought conditions on the river you are planning on traveling on.

Bring several different paddles. I like a double bladed paddle in the wind and going upstream. Your ability to eddy hop will have a lot to do with your rate of travel. Since a canoe or kayak can only travel at a sustained speed of 3-5 mph or less, any current above that will stop you in your tracks. The lower parts of the rivers in South America are affected by tides which can work to your advantage if you understand tides.

Tributaries tend to have higher gradients and velocities than the rivers they flow into.
There are a few books about long canoe trips in South America, but they are few and far between.

There are two groups of people that attempt trips like the one you are contemplating. Really experienced people that know exactly what they are getting into and inexperienced people that have little idea what they are getting into. You may be in the second group. I would rethink your plan.