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Port Jefferson/Mount Sinai

New York, United States
AOW suggested27–29 m (88–94 ft) depthBoat entry7mm or semi-dry + hood typical

Boat dive — see Entry & access.

Port Jefferson/Mount Sinai at a glance

Port Jefferson/Mount Sinai is an advanced boat dive site in New York, United States with depths of 26.8–28.7 m (88–94 ft). Typically most favorable May–Jul · from 3 years of archive data. Divers commonly see Black sea bass, Cunner, and Tautog (blackfish). Recent reports put the water around 17°C (62°F). Check the latest conditions and entry details before you go.

No window today· next: tomorrow 8:00–18:00 · favorable

Forecast for this hour · 20:00 · run 19 h ago
0.1 m (0.5 ft)waves — under half a meter expected (waves — under a foot expected)

Tap a factor for its source and model point · Forecast 17°C · seasonal avg 18°C ( · Forecast 62°F · seasonal avg 65°F)

Site hazards: Depth (~90 ft) and Long Island Sound current; cold/dark at depth; limited visibility; boat traffic; fishing tackle.

Read the full hazards ↓

Dive windows this week

MonNo window

0.2 m waves · 10 kn wind (0.7 ft waves · 10 kn wind)

Tue8:00–18:00 favorable

0.4 m waves · 12 kn wind (1.3 ft waves · 12 kn wind)

Wed8:00–18:00 favorable

0.1 m waves · 5 kn wind (0.2 ft waves · 5 kn wind)

Thu8:00–18:00 favorable

0.1 m waves · 8 kn wind (0.2 ft waves · 8 kn wind)

Fri8:00–18:00 favorable

0.2 m waves · 10 kn wind (0.7 ft waves · 10 kn wind)

Sat8:00–18:00 favorable

0.1 m waves · 6 kn wind (0.2 ft waves · 6 kn wind)

Sun8:00–18:00 favorable

0.0 m waves · 7 kn wind (0.1 ft waves · 7 kn wind)

Favorable windowModerate window— no window

Every forecast dive window each day, site-local time, from wave and wind forecasts. Numbers under each bar are daylight averages.

First light 6:48 · Sunrise 7:16 · Sunset 17:55 · some windows run past sunset

Source: Open-Meteo marine · model point 6.9 km from site · updated 26 Oct, 01:27 GMT-4

Forecast only — always assess conditions on site.

Compare this weekend’s windows near Port Jefferson/Mount Sinai

Forecast · NOAA tide model

Tide & slack timing

Loading tide predictions

Recent diver reports

Dated firsthand observations from divers — not current conditions.

No diver reports for this site yet. — one dated observation helps every diver after you.

Dived here today — did the forecast match?

What Divers Say

Known for: Black sea bass, Cunner, Tautog (blackfish)
Best time: Summer on slack tide; manage depth and bottom time.

Based on community reviews and site data. Conditions vary — always verify before diving.

Best months, historically

What conditions have historically been typical at this site, month by month — not a forecast.

  1. January, 94% of days have historically been favorable, water has typically been 5°C (41°F), waves have typically been 0.6 m (2.0 ft), wind has typically been 13 knots
  2. February, 95% of days have historically been favorable, water has typically been 4°C (39°F), waves have typically been 0.5 m (1.7 ft), wind has typically been 13 knots
  3. March, 91% of days have historically been favorable, water has typically been 5°C (41°F), waves have typically been 0.6 m (1.8 ft), wind has typically been 13 knots
  4. April, 96% of days have historically been favorable, water has typically been 8°C (47°F), waves have typically been 0.5 m (1.7 ft), wind has typically been 12 knots
  5. May, 100% of days have historically been favorable, water has typically been 13°C (56°F), waves have typically been 0.4 m (1.2 ft), wind has typically been 11 knots, historically most favorable
  6. June, 100% of days have historically been favorable, water has typically been 18°C (65°F), waves have typically been 0.3 m (1.0 ft), wind has typically been 10 knots, historically most favorable
  7. July, 100% of days have historically been favorable, water has typically been 24°C (74°F), waves have typically been 0.2 m (0.8 ft), wind has typically been 9 knots, historically most favorable
  8. August, 99% of days have historically been favorable, water has typically been 23°C (73°F), waves have typically been 0.3 m (1.1 ft), wind has typically been 10 knots
  9. September, 98% of days have historically been favorable, water has typically been 22°C (71°F), waves have typically been 0.4 m (1.2 ft), wind has typically been 10 knots
  10. October, 96% of days have historically been favorable, water has typically been 18°C (65°F), waves have typically been 0.5 m (1.6 ft), wind has typically been 11 knots
  11. November, 93% of days have historically been favorable, water has typically been 14°C (57°F), waves have typically been 0.6 m (1.9 ft), wind has typically been 13 knots
  12. December, 92% of days have historically been favorable, water has typically been 8°C (46°F), waves have typically been 0.6 m (1.9 ft), wind has typically been 13 knots

May, June, and July have typically had the largest share of favorable days here. Conditions vary year to year — this is historical context, not a forecast.

Based on 3 years of archive data. Bar height shows the share of days each month whose conditions have historically scored favorably.

Marine life seen at this site

Species noted at this site — not a promise of what you’ll encounter.

Species seen here

Rough labels: “Commonly seen” usually means two or more recorded sightings near this site in public dive logs (GBIF), “Occasionally seen” one; “Seasonal” and “Rarely seen” come from dive-guide research. Not a measured rate.

Fills & rentals nearby

Facts from OpenStreetMap, corrected by the community — listed by distance only. Details change; confirm with the shop.

Shop facts come from OpenStreetMap and community corrections, shown nearest first. PickADive lists facts and contacts only — no listing is sponsored or ranked.

Data updated June 2026

Site details

The Port Jefferson/Mount Sinai Reef is a 50-acre NYSDEC artificial reef in Long Island Sound about 1.79 nautical miles northeast of Port Jefferson Inlet, in 88-94 ft of water. Built from a barge and concrete buoy sinkers with concrete blocks added in 2025, it is a deep Sound reef best suited to advanced/deep divers. Black sea bass, tautog and scup hold on the structure; visibility is variable.

boatreef

Depth (~90 ft) and Long Island Sound current; cold/dark at depth; limited visibility; boat traffic; fishing tackle.

Reviews

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