For the pony swim, the Saltwater Cowboys round up feral Chincoteague ponies, that have been put in pens days earlier, from the Virginia side of Assateague Island and drive them across the Assateague Channel to Veteran's Memorial Park on Chincoteague Island.

The National Park Service, which controls the ponies on the Maryland side of Assateague, claims that the horses were brought to the island in the 17th century;[3] however, leaders of the Chincoteague Volunteer Fire Company, which owns the ponies on the Virginia side of Assateague,[3] claim that the horses are descended from Spanish horses who swam to the island from a shipwrecked Spanish galleon off the Virginia coast on their way to Peru in the 16th century.

[4] By the 1700s, the pony penning was an annual event and unclaimed animals were branded or marked for ownership by groups of settlers.

In 1909, the last Wednesday and Thursday of July were designated as the annual days for pony penning.

In 1924, the first official Pony Penning Day was held, where the foals were auctioned at $25–50 each to raise money for fire equipment.

Fish and Wildlife Service which allows the fire department to let the horses graze on the Virginia side of Assateague Island.

Members of the Chincoteague Volunteer Fire Department known as "Saltwater Cowboys" oversee the annual pony swim.

[16][15] During spring roundups, the Saltwater Cowboys also release buyback ponies from the previous year's auctions.

[17] In the winter of 2018, the Saltwater Cowboys had to euthanize seven ponies suffering from "swamp cancer," a fungal infection.

[18][19] After the loss of these ponies, three mares with ancestral roots on Assateague were donated to the Saltwater Cowboys in order to help maintain the herd population.

[20][21] There has since been leaps and bounds in the research of "swamp cancer", and many ponies have now been able to be treated for it and released back onto the island.

Prior to the swim, the Saltwater Cowboys round up the north and south herds on the island and put them into corrals.

[12][24] Usually, a television screen is located at Veterans Memorial Park so that those in the back of the crowd can still see the swim.

[25] The ponies rest for a short period while they are examined by veterinarians and are then driven along Ridge Road on a parade route to the Volunteer Fire Department Fairgrounds by the Saltwater Cowboys.

These ponies leave the fairgrounds in the morning and then swim back across the channel by noon, guided by the Saltwater Cowboys.

Volunteer fire department personnel responded to say that the death was a "freak accident" and that future events would not be cancelled.

The annual auction is a fundraiser for the Chincoteague Volunteer Fire Department and is also used to maintain the herd size.

Fish and Wildlife Service allows them to graze a herd of up to 150 horses, the department uses the auction as a way of keeping the numbers within the limits of the permit since approximately seventy to one hundred foals are born each year.

[16][29] The charity was created in 2003 in memory of Carollynn Suplee, who used to attend the auction to help children buy ponies until she died from cancer.