At the mouth of rivers, where they enter lakes and oceans, deltas form from sediment the water no longer had energy to carry. River energy is supplied by gravity, as the water flows from high elevations to lower elevations. The steeper the elevational gradient, the faster the water moves and the more energy it carries. More water also carries more energy, so a flooding stream can transport more sediment than the same stream at normal water levels. Depending on their energy, rivers transport a wide range of particles as their sediment load, from clay-sized glacial flour to large granite boulders.
Lakes have energy supplied by wind and density currents.
Wind creates waves that stir up sediment in the shallows and move it, usually towards and away from shore. Wind also generates surface currents that move sediment along shore. Like rivers, density currents are driven by gravity and can be thought of as internal rivers. Just as rivers flow down elevational gradients, so lake water flows down density gradients creating a current as it moves. Density gradients are formed by differences in temperature, sediment load, or dissolved mineral load.