According to Bernoulli's principle, where the speed of a fluid is high, its pressure is

Explanation

Since the total energy per unit volume is fixed, any gain in kinetic energy must be paid for by a fall in pressure energy. This is why a shower curtain is pulled inwards by the fast moving water stream and why two ships moving side by side are drawn together. The effect is easy to state and easy to misremember, so it is heavily tested.