The Great Lakes have beaches with real surf, large dune systems and hazardous currents. The behavior follows from scale, since fetch rather than salinity is what produces waves.
Fetch is what builds a wave
Wind transfers energy to water over distance. Given hundreds of miles of open water, a sustained wind builds waves of a size most people associate with a sea coast.
Several of the lakes offer that distance along their long axes, so an autumn wind blowing the length of a lake produces genuine surf at the downwind shore.
Salinity has essentially nothing to do with it. Fresh water is slightly less dense, which affects buoyancy marginally, but wave generation works the same way.
The waves are shorter and steeper
Lake waves are generated locally rather than arriving as long-period swell from a distant storm, so they are closer together and steeper for their height.
That makes conditions build and subside quickly. A lake shore can go from flat to rough within hours and back again, which open ocean coasts rarely do.
It also makes the waves less orderly, since a locally generated sea contains a mix of periods rather than clean sets.
Dunes form for the same reasons they do on a sea coast
Wind moving sand up a beach and vegetation trapping it builds dunes wherever there is a sand supply and a prevailing onshore wind, and parts of the lakes have both in abundance.
Some of the largest freshwater dune systems anywhere sit on these shores, and they are managed much like coastal dunes, with marked crossings to protect the stabilizing vegetation.
The currents are a serious hazard
Structural currents form along the lakes in the same way they do on the ocean: water pushed shoreward by waves returns seaward through channels, along piers and around structures.
Piers and breakwalls are a particular concern, because water moving along a structure can carry a swimmer away from shore quickly. Many lake drownings are associated with them.
Beach flag and warning systems operate on lake shores, and the guidance from lifeguards, park staff and official water safety agencies is the authority on any given day.
What differs from a sea coast
There is no meaningful tide, so the water line stays where it is, and seasonal water level changes happen across years rather than hours.
Water temperature stratifies sharply in summer, and a wind shift can replace warm surface water with much colder water from below, which is a real factor for swimmers.