Water can flow uphill in a formation known as a hydraulic jump. These phenomena are most visible in two types of locations:

1. In some rapids, the speed of a river drastically decreases when fast-moving water discharges into a slow region of the river. If the speed of the water is greater than a certain threshold (see the linked article above for calculation of this speed), the force that the fast water exerts as it slows down can force the following water to rise slightly.

2. Some dam spillways use an engineered hydraulic jump to slow the speed of the water coming off the spillway. These represent a best-case scenario: the spillway is a smooth, low-friction surface, and it usually is a long, steep fall with the jump directly at the bottom (no horizontal distance for energy to be lost). However, even under ideal conditions the jump will be tiny compared to the initial fall. Even a "ski jump" type spillway, where the water is launched into the air, achieves very little height.

Finally, as Serban alluded to in a (now deleted) comment, if the speed of the water is high enough to force it uphill over any significant distance, it will tend to erode the obstacle over time, or push out of the riverbed and flow around the obstacle. (See the answers to this question for some of the problems associated with trying to naturally constrain high-pressure water.)

Water can flow uphill in a formation known as a hydraulic jump. These phenomena are most visible in two types of locations:

1. In some rapids, the speed of a river drastically decreases when fast-moving water discharges into a slow region of the river. If the speed of the water is greater than a certain threshold (see the linked article above for calculation of this speed), the force that the fast water exerts as it slows down can force the following water to rise slightly.

2. Some dam spillways use an engineered hydraulic jump to slow the speed of the water coming off the spillway. These represent a best-case scenario: the spillway is a smooth, low-friction surface, and it usually is a long, steep fall with the jump directly at the bottom (no horizontal distance for energy to be lost). However, even under ideal conditions the jump will be tiny compared to the initial fall. Even a "ski jump" type spillway, where the water is launched into the air, achieves very little height.

Finally, as Serban alluded to in a (now deleted) comment, if the speed of the water is high enough to force it uphill over any significant distance, it will tend to erode the obstacle over time, or push out of the riverbed and flow around the obstacle. (See the answers to this question for some of the problems associated with trying to naturally constrain high-pressure water.)