Seaweed
Archimandrite Nikifor’s Biblical Encyclopedia
(Jonah 2:5) - marine vegetation grew abundantly from ancient times along Mediterranean shores. The source says that the Arabian Gulf was called the Red Sea because abundant seaweed gave its waters a red-green appearance. Another kind of river growth was the Nile reed or rush, which grew profusely along the Nile; among it Moses' mother once hid the infant in a reed basket (Exod 2:3, 5).