Isthmus Reef - California
Isthmus Reef, right off Catalina, is a mellow introduction to California diving. It’s shallow, capping out around 16 meters, which makes it perfect for knocking off some rust or getting comfortable with temperate water. We’ve always found it a solid spot for spotting a leopard shark tucked into the kelp, and the schooling opaleye can be pretty mesmerising as they swirl around the giant bladder kelp. Visibility can be hit or miss, typical for SoCal, but when it's good, it’s a lovely, easy dive.
- Location
- California, United States, North America
- Coordinates
- 33.446100, -118.494100
- Type
- reef
- Maximum Depth
- 16m
- Difficulty
- Beginner
Marine Protected Area: Cat Harbor (Catalina Island) State Marine Conservation Area
Best Time to Dive in California
The warmest water temperatures in California occur in August, averaging 20.6°C (up to 24.0°C). The coolest conditions are in February at 14.0°C.
The calmest sea conditions are typically in July with average wave heights of 0.60m.
Monthly Water Temperatures
- January: 14.4°C (air: 14.0°C)
- February: 14.0°C (air: 13.8°C)
- March: 14.2°C (air: 13.3°C)
- April: 14.9°C (air: 14.3°C)
- May: 16.6°C (air: 15.4°C)
- June: 18.9°C (air: 17.4°C)
- July: 20.4°C (air: 18.9°C)
- August: 20.6°C (air: 19.6°C)
- September: 20.4°C (air: 19.7°C)
- October: 18.8°C (air: 18.4°C)
- November: 16.3°C (air: 16.0°C)
- December: 15.6°C (air: 14.3°C)
Nearby Dive Sites in California
Nearest Dive Centres to Isthmus Reef
- Adventure Sports Unlimited - PADI
- Adventure West Scuba - PADI
- Aloha Scuba
- Anderson's SCUBA diving
- Any Water Dive Center - PADI, DAN
- Aquanautics Dive, Inc - ["PADI"]
Marine Life in California
Home to 10 recorded species including 8 reef fish, 1 other, 1 octopus & squid.
Notable Species
- Vernal Pool Fairy Shrimp (Branchinecta lynchi)
- Rainbow Trout (Oncorhynchus mykiss) - Reef Fish
- Western Mosquitofish (Gambusia affinis) - Reef Fish
- Sea Trout (Salmo trutta) - Reef Fish
- Little post horn squid (Spirula spirula) - Octopus & Squid
- Prickly sculpin (Cottus asper) - Reef Fish
- cutthroat trout (Oncorhynchus clarkii) - Reef Fish
- Striped Bass (Morone saxatilis) - Reef Fish
- brook trout (Salvelinus fontinalis) - Reef Fish
- Ribbonfish (Lepidopus caudatus) - Reef Fish
Recommended Packing List for Isthmus Reef
Based on average water temperature of 17.1°C.
- Wetsuit (5-7mm) - recommended for 17°C water
- Hood & Gloves (3-5mm) - helps retain warmth
- Mask - essential for every dive
- Fins
- BCD - buoyancy compensator
- Regulator - your most safety-critical piece of gear
- Dive Computer - tracks depth, time, and NDL
- Surface Marker Buoy (SMB) - essential for boat pickups
- Dive Torch - useful for crevices and colour at depth
- Underwater Camera - capture your diving memories