Mnemba Atoll · Tanzania · Wall · Cave & cavern
Jackfish Alley
A cavern at 35 m with jacks schooling off the wall
Area photo: Jorge Láscar · CC BY-SA 2.0
Jackfish Alley is a deep drop-off in open water east of Mnemba Atoll, starting at 24 metres and falling to roughly 60. Its distinguishing feature is a cavern at 35 metres that is always full of fish, and the schooling jacks the site is named for come up out of the deep water alongside the wall.
Where it is and how deep
5.8171° S, 39.4168° EPublished position for this site.
The dive
Nothing about this site is shallow. The drop-off starts at 24 metres and falls from there to roughly 60, so the descent goes straight to depth and the dive is worked along the wall on a tight time budget. Plan the profile and the turn pressure before you get in, because the face keeps going well past any recreational limit and offers no natural place to stop.
The feature that sets the site apart is a cavern at 35 metres, reliably full of fish with several species stacked into the one piece of shelter. Snappers of every colour, lobsters and titan triggerfish live near the wall around it. Keep an eye on the open water as well: schools of jackfish come up out of the deep along the face, and they are what the site is named for.
Depth sets the shape of the dive here. The drop-off offers nothing shallower than 24 metres, so the ascent and the safety stop are planned in advance rather than improvised over a reef top. It is a poor choice for the first dive of a trip and a good one once weighting and gas consumption have settled.
Marine life and season
- Trevally & jacks
- Reef fish swarms
- Macro critters
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Good | Off-season | Off-season | Fair | Good | Good | Good | Prime | Prime | Prime |
Season follows Mnemba Atoll: Jul–Mar is divable, with Dec–Feb calmest and clearest; the long rains in April and May bring poor visibility and rough crossings.
Know before you go
- The wall runs to about 60 metres and the site's main feature sits at 35 m, so the whole dive is deep; agree a hard maximum depth and turn pressure before descending.
Questions divers ask
How deep is Jackfish Alley?+
The drop-off starts at 24 metres and falls to around 60. The cavern that the site is known for is at 35 metres, so a normal dive here sits in the 24 to 35 metre band.
Sources
- Jackfish Alley — Dive Site — Scubago
More dive sites in Mnemba Atoll
Wall
A vertical face from 18 m to 50 m, cut with caves and overhangs
Reef
A glassfish shelter at 25 m on the atoll's busiest reef
Seamount
A sea mount topping out at 14 m and dropping to 50 in strong current
Wall
A second drop-off at 30 m hung with gorgonians
Plate corals along the north edge of a 20 m bommie slope
Similar dives elsewhere
The sand floor beside the wall drops away past 80 m
Two archways cut through the wall of a sunken bowl
An archway in the rock wall, ringed by reef fish
A wall to 40 m off a 5 m reef, with a double arch at 20 m