Red tide and Saltwater

Red tide noun - Seawater that is discolored by large numbers of certain dinoflagellates that produce saxitoxin.

Saltwater and red tide are semantically related. In some cases you can use "Saltwater" instead a noun phrase "Red tide".

Saltwater noun - Water containing salts.

Red tide and saltwater are semantically related. Sometimes you can replace phrase "Red tide" with "Saltwater", this terms are similar.