Water polygons representing the lake and river.Water areas are filtered and simplied acoording to scalerank and osm_area. At lowest zoom levels, it just has big lakes and give rivers.When you zoom in, more small water area should show up.

The 'class' field indicates the value of the water, the possible values are: 'ocean' , 'lake' , 'natural' , 'river' , 'pond' , 'pool' , 'reservoir' , 'basin' , 'canal' , 'lock' , 'swimming_pool' .