The S-Curve at Gates of the Mountains is a dramatic section of the Missouri River canyon featuring steep walls and underwater cave formations. This freshwater site requires boat access and is suited for advanced snorkelers due to moderate currents, cold water, and significant depths. The average depth is 8 metres, though the canyon floor drops further. Snorkelers should remain vigilant for boat traffic throughout the area. Facilities including parking and toilets are available near the site. The experience is defined by the unique geological formations of the canyon walls and the deep, open water environment.

Coulter Campground in the Gates of the Mountains offers a freshwater drop-off experience accessible only by boat. The site features a prominent overhanging rock wall that descends into a pool reaching depths of approximately 9 metres. Divers and snorkellers should be prepared for variable conditions, including cold water and potential thermoclines. Due to the nature of the terrain and the requirement for boat access, this site is best suited for intermediate divers. Toilets are available at the campground for visitor use. As this is a freshwater environment, divers should be aware of the potential for low visibility and entanglement hazards.

Departure Point Beach is a day-use area located within the Gates of the Mountains. This freshwater site features a small beach entry, making it accessible for beginners looking for a quiet snorkeling experience. The area is situated south of Log Gulch and provides basic facilities including parking and toilets. Divers and snorkellers should remain aware of boat traffic in the vicinity and be prepared for cold water temperatures. Conditions at this site can vary, and it is recommended to exercise caution due to the presence of watercraft. The site offers a peaceful environment for those exploring the shoreline of Holter Lake.

Log Gulch, located within the Gates of the Mountains, offers a freshwater snorkeling experience featuring a designated, enclosed swimming area. This protected zone provides a safer environment for snorkelers by separating them from motorized vessels. The underwater terrain consists of submerged rocks and aquatic vegetation. The site is accessible via a shore entry and is suitable for beginners, though conditions vary. Water temperatures are very cold, reaching 1°C, which impacts local fish behavior. The area is open seasonally from Memorial Day through Labor Day. Facilities available on-site include parking, toilets, showers, changing rooms, and a rinse station. Divers and snorkelers should be aware of potential hazards including cold water and entanglement.

Hauser Causeway is a shallow artificial reef site located where Lake Helena meets the Hauser Reservoir. Divers and snorkellers can expect depths ranging from 1 to 4 metres, with an average depth of 2 metres. Conditions are characterised by mild currents and low visibility, typically between 1 and 3 metres. The water is very cold year-round, with temperatures recorded as low as 0.5°C in early April, making drysuits or thick wetsuits essential. Access is available via both shore and boat. Due to the potential for boat traffic, cold water, and limited visibility, divers should exercise caution. Facilities at the site include parking, toilets, and a cafe.

White Sandy Recreation Area is situated at the confluence of Prickly Pear Creek within the Gates of the Mountains. This freshwater site features a sandy shore entry and provides views of the Big Belt Mountains. Divers and snorkellers should be aware of variable conditions, including low visibility and distinct thermoclines. Deeper water remains cold, often ranging between 4 and 9 degrees Celsius, due to stratification and river inflow. The mixing of creek and lake water creates temperature gradients throughout the site. It is suitable for beginners and offers accessible facilities including parking and toilets.

Devil's Elbow, located within the Gates of the Mountains, offers freshwater diving and snorkelling access from a small beach at the campground. The site features drop-offs near the boat docks, with depths ranging from 5 to 21 metres and an average depth of 8 metres. Conditions include mild currents, though water temperatures can be very cold, particularly in spring and at depth, presenting a risk of hypothermia. Divers should remain aware of boat traffic in the area. Facilities at the site include parking, toilets, and a cafe. Typical dives last approximately 45 minutes. This site is best suited for intermediate divers, while snorkelling is rated 2 out of 5.

Clark's Bay is a freshwater reef site located within the Gates of the Mountains, offering a roped-off sandy beach for easy shore entry. The site features shallow water, making it suitable for beginner snorkellers. Conditions at the site are variable, with mild currents and potential for low visibility. Divers and snorkellers should be aware of the cold water temperatures and the presence of a thermocline, which pose a risk of hypothermia outside of peak summer months. Boat traffic is a known hazard in this area. Facilities available at the site include parking and toilets.