Can the grease in my boat trailer wheel bearings contaminate the water?

In some locations, there are strict regulations to protect water from contamination. For those cases, there are specialty lubricants formulated with biodegradable base fluids and environmentally friendly additives.  In other cases, greases that are designed for wheel bearing lubrication have been found to be suitable.  Those products have reasonably good resistance to water, and typically do not readily dissolve in water.