The Buzzard Bay Coalition’s annual open water swim is still months away, but Gleason Family YMCA Aquatics Director Mel Dyer’s training classes are completely full.

“It’s twelve people for the [advanced] class, and for the other class we had limited it to six, but it filled up right away,” Dyer said. “We will probably expand that for next year.”

It will be Dyer’s fifth year with the Y, and her fifth year doing the open water swim, which will be held June 25. She said it was the first community event she signed up for when she moved back to the area.

“I saw it advertised … and I thought, ‘Well, if I am going to be qualifying people for this, then this is something I should be doing myself,’” Dyer said.

There are significant qualifications for participants in both levels of Dyer’s class. The intermediate students must be able to swim 200 yards continuously, in freestyle and one other stroke. The advanced students must swim 500 yards continuously, and have a “strong grip” on their strokes. The latter group usually comes from a swim team background.

Dyer herself started out open water swimming, and prefers it to pool swimming. As a child, she said her parents would take her and her siblings swimming often, and she grew up learning to swim in Rochester every summer when school let out.

“We were at the beach pretty much all summer long,” Dyer said. “It’s where I met my friends, it’s where I met my mentors, the lifeguards. So, most of my experience has been at the beach.”

Dyer is currently training two classes of swimmers for the open water swim. One is the advanced class, and the other is the intermediate to lower class. Originally, she said there was just one class, but decided to split the class into two because of the demand for spots in the class and the variance in swimming ability within the class itself.

“I have swimmers who think nothing of spending hours in the pool, swimming back and forth – can tuck away ten miles at a time,” Dyer said. “

There are significant differences between swimming in the open water and swimming in a pool, Dyer said. Whereas a pool is generally calm and of even temperature, open water can be much different.

“You don’t have a line on the bottom, where the depth changes, where you can’t see the bottom, where the temperature changes through thermoclines, where there might be things in the water – it throws them,” Dyer said. “Open water swimming can be a challenge, not only for the mental aspect, but also the physical one.”

Dyer also said the wind and wave conditions can drastically change from moment to moment in the ocean.

“It can go from being perfectly peaceful to really turbulent in very little time,” Dyer said. “There are years that we start and there’s waves, and there’s chop, and by the end it’s perfectly calm and peaceful and it’s like, ‘I wish I had been in the last wave!’”

The trade off is that a swimmer will sink more easily in a pool than in the ocean due to the ocean’s salt content.

Dyer said it is always “very rewarding” to see her students finish the open water swim because “it is a challenge.”

“You can swim in a lake, you can swim in a pond, but the ocean – the ocean is its own animal,” Dyer said.

The swim will take place June 25 at the Outer New Bedford Harbor. For more information, visit http://support.savebuzzardsbay.org.