Halacha Orach Chaim 228

When one sees wondrous mountains rivers or deserts, a Bracha of Oseh Maaseh Beraishis should be recited. These Brachos are only recited upon seeing a natural phenomenon that is uncommon. Reb Shlomo Zalman rules that someone who lives near one of these natural phenomena, and they have become commonplace for him, should not recite this Bracha.

Upon seeing The Yam Hagadol, one is to recite a Bracha of Oseh Yam Hagadol. There is a disagreement what exactly the Yam Hagadol is.

According to the Mechaber, the Bracha is recited on seeing the Mediterranean sea. According to other Poskim, the Bracha is recited upon seeing the great oceans that surround the world. Dayan Fisher follows this second opinion. However, he adds that when reciting the Bracha of Oseh Maaseh Beraishis on the Mediterranean sea, one should make a point of adding the phrase Oseh Yam Hagadol upon completion of the Bracha.