Isthmus Deep

Text and photos Copyright 1995 By Eric Maiken and Joe Dovala

A view from north of Catalina Island's Two Harbors illustrates the stepped reefs and islets off of  Isthmus Cove.  

From the fallen tower off of the red rock stripe at Blue Cavern to Ship Rock's deep ring and finger reefs, the area hosts a number of excellent deep diving sites --all close to the hyperbaric facility at Big Fisherman's Cove. 

The steep terrain of the Island and offshore rocks makes for dramatic diving as well as scenic decompressions in the shallow kelp forests.




Click Image to View a Scaled Plot 

Tower Base I-beams lead down slope to the tower bell.


Flange on top of  the bell where the sub coupled to the lock-out chamber above the bell.


The Tower
Apart from a few Island locals, the former test platform for the Beaver submarine was largely forgotten as a dive site for nearly two decades. In 1990, the tower was rediscovered when a boat fouled  it's anchor on one of the mooring cables that anchored the structure to large concrete blocks. At that time, the tower stood upright a few hundred feet offshore, with the bell's lockout hatch at 130 fsw, and the base at 195 fsw. The skyscraper's silhouette against the blue water had an otherworldly appearance.

In 1992, a Great White shark approached two trimix divers, who then started the local tradition of abandoning anchor line decompressions in favor of swimming inshore to the kelp beds off Blue Cavern.

Sometime during the spring of 1993, an anchor caught and broke the tower's western rigging, causing the structure to fall perpendicularly to shore. The bell landed in 210 fsw near deep patch reef. In the years since its demolition, the tower's neighborhood has declined. Gone are the schools of fish that once swirled in the water column above the structure. The carpet of yellow zoanthid anemones that covered the bell and grated deck have been displaced by silt.

While still a good dive, the twisted I-beams of the tower's base point up-slope to the bright, living reef, where the best part of the decompression dive awaits.

Ring Reef
The northwest corner of Ship Rock falls steeply to a sandy incline that begins in 165 fsw. Down slope, a series of reefs arc like stepped retaining walls, holding the sand back on one side, while dropping abruptly to the next level on the other. On the ring reef at 225 fsw, chimney sponges hide rock fish that peer curiously out at divers. The north face is equally entertaining, with long rock fingers projecting into deep water. Here, the sand also slopes steeply, bringing 300 fsw deep water to within a few hundred feet of the rock. Decompression on the rock walls rewards divers with some of the finest shallow water in California. Walls of invertebrates, schools of baitfish, and the occasional pelagic surround the rock.

Bird Rock Wall
The northeast side of Bird Rock tumbles down in a series of stepped ledges, beginning with a gorgonian-covered wall at 60 feet, and continuing below 200 feet. While not as lively as the slope off Ship Rock, the sand is littered with relics lost by the past century's boaters, fishermen, and divers.







Ship Rock Decompression. The 200 foot wall on the north western side of Ship Rock Is a great place to stage decompression stops. This shot is in the kelp forest that covers the upper regions of the rock.



Caged Sharks. A number of illegal lobster traps used to be scattered in deep water on the northern end of the rock. These two Horn Sharks were found trapped at 190 feet. We let them go,  broke up the cage, and sent a letter to Cal Fish and Game.