In the area of water beneath the tug, we can see that Turner sometimes painted quick, sketchy marks as finishing touches to his work. They are a kind of visual short-hand, particularly effective when viewed at a distance. Here, rapidly-painted squiggles suggest the way that reflections are broken up by the rippled surface of the river.
The thick, crusted areas of paint are known as impasto, a technique that made the most of oil paint's plastic qualities. Turner sometimes used a palette knife to achieve this effect, but here, the rounded dabs of paint suggest that he worked with a heavily loaded brush instead.