New England, United States
    Henry Cabot Lodge Bird Sanctuary (Egg Rock)

    Three and One-half Fathom Ledge

    Best months: Jul–Sep

    Protected Area

    Henry Cabot Lodge Bird Sanctuary (Egg Rock)

    Why dive here

    With 35+ marine species recorded in the area - including nurse sharks - Three and One-half Fathom Ledge offers some of New England's richest reef diving. Water ranges 4-19°C, warmest July, August, September.

    Best timeJul–Sep
    WetsuitA 5mm wetsuit
    Marine lifeNurse Sharks · 35+ species recorded
    Water4-19°C · warmest July, August, September
    CharacterReef dive

    Three and One-half Fathom Ledge. Don't let the name fool you, there’s more to this New England spot than a shallow measurement. We love a good rocky reef, and this one delivers with dramatic drop-offs and crevices that shelter some fascinating cold-water characters. Forget the tropical clichés; here, it’s all about the texture of the rock, the way the light filters through kelp, and the surprising resilience of life in a colder ocean. You’ll often find Black Sea Bass lurking in the shadows, and we’ve spotted the occasional Porbeagle shark cruising the deeper edges – a real thrill. Keep an eye out for the Star Ascidian, which adds a splash of unexpected colour against the drab rock. It’s a site that rewards slower diving, letting your eyes adjust to the nuances of the environment. Strong currents can pick up here, so we always plan our dives around slack tide, which generally means better visibility and a more relaxed experience. This isn't a drift dive; it's a place to anchor yourself and explore.

    Safety Notes

    Cold water this month (avg 15°C). Drysuit or thick wetsuit (7mm+) recommended.

    Today05:5117:1111h 20m daylightGolden hour 16:33

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    Conditions

    Ocean conditions, forecast and tides for Three and One-half Fathom Ledge

    Three and One-half Fathom Ledge Ocean Conditions

    Monthly averages for Three and One-half Fathom Ledge, sourced from Open-Meteo marine data - nearest station: Open-Meteo marine grid (42.6, -70.6) (0km away)

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    October Averages

    Sea Temperature

    15°C

    59°F · Range: 12.8–18.1°C

    Air Temperature

    10°C

    50°F

    Wind Speed

    3.78 m/s

    7.3 knots

    Atmospheric Pressure

    1017 hPa

    Based on 4 years of monitoring data · Data sources: Open-Meteo marine data

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