freshwater vs hydrographic

freshwater

adj
  • Consisting of fresh water. 

  • neoclassical, in reference to U.S. macroeconomics and economics departments near the Great Lakes. 

  • Unskilled as a seaman. 

  • Living in fresh water. 

noun
  • A body of fresh water 

hydrographic

adj
  • Of or pertaining to hydrography. 

How often have the words freshwater and hydrographic occurred in a corpus of books? (source: Google Ngram Viewer )