Avacha Bay (Russian: Авачинская губа, Авачинская бухта) is a Pacific Ocean bay on the southeastern coast of the Kamchatka Peninsula. It is 24 km (15 mi) long and 3 km (2 mi) wide (at the mouth), with a maximum depth of 26 m (85 ft).^[1]

The Avacha River flows into the bay. The port city of Petropavlovsk-Kamchatsky and the closed town of Vilyuchinsk lie on the coast of the bay. It is the main transport gateway to the Kamchatka region. The bay freezes in the winter.

It was first discovered by Vitus Bering in 1729. It was surveyed and mapped by Captain Mikhail Tebenkov of the Imperial Russian Navy in the 1830s.^[2]

Avacha Bay has been the scene of massive die-off of benthic marine organisms in September–October 2020.^[3][4][5]

The Avacha Bay is uiquqe in that it is among the largest bays in the world able to fit any ship in the world.^{[citation needed]} It is an internal part of Avacha Gulf. Total area is 215 square kilometers. Depth – up to 26 meters. Main rivers flowing into the bay – Avacha and Paratunka. It is the home base of the Russian Pacific fleet.

• Tri Brata – "Three brothers", a major landmark in the bay
• Petropavlovsk-Kamchatsky
• Nikolskaya sopka