The Network Analyst tools require points as input. To find the network distance from a lake or river, you would want to use the OD cost matrix solver, but you can't load a polygon or line feature class for Origins or Destinations. They have to be points. You can convert your polygons or lines to point features by finding the centroids of those features, by using the features' nodes, by finding the intersecting points of your streets features (if they intersect at all), or by manually digitizing river/lake access points along the roads.