When boating in an area that has no posted speed limit what determines the legal speed?

The conditions and circumstances at any given place and time determine the speed. While there may be no speed limits on boats in certain areas, under all boating regulations, boats must be driven only at safe speeds. The boater must take into account all of the conditions and circumstances in order to determine the proper speed. If a boater were in an unposted speed area at night, in fog with many other boats in the areas, he/she would not be permitted to go as fast as he/she wanted to go.