estuary vs lagoon

estuary

noun
  • An ocean inlet also fed by fresh river water. 

  • A coastal water body where ocean tides and river water merge, resulting in a brackish water zone. 

lagoon

noun
  • A shallow body of water separated from deeper sea by a bar. 

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