Learn Russian: Мы будем долго плутать, если пойдём болотом. - We will wander for a long time if we go through the swamp.

This is the Bare Instrumental of Route. In Russian, you can describe the physical space or terrain you are moving through by putting it directly into the instrumental case, like болотом (through the swamp) or лесом (through the forest). It focuses on the environment you use as your path.

Could we say через болото or по болоту instead of болотом?

Yes, they are very similar but have slight nuances. Через болото emphasizes crossing the swamp from one side to the other. По болоту focuses on moving along the surface of it. The bare instrumental болотом emphasizes the swamp as the overall route and is very common with open natural terrains.

Why do we use the perfective пойдём in the if-clause, but the imperfective будем плутать in the main clause?

The perfective пойдём establishes the completed condition: if we make the choice to take this route. The imperfective будем плутать describes the ongoing process that results from it: we will be wandering around continuously. The word долго (for a long time) is a strong trigger for the imperfective aspect here.

Does плутать mean the same thing as блуждать?