The Chas Lap

The “Chas Lap” is a near-perfect open water swim workout: an end-to-end tour of the Greater Aquatic Park swimming terrain that doesn’t need an escort craft; 2 statute miles across, against, and with current, for a 60-90 minute adventure for most swimmers on most days.

After a quarter-mile warmup from the SERC/Dolphin beach to the Aquatic Park cove opening, the Chas Lap kisses the entrances to the two marinas bookending Aquatic Park - Hyde Street marina to the east, and Gashouse Cove marina to the west. (Beyond these points, swimmers are not advised to swim unescorted.) Then a return to the Opening and a final quarter-mile cool-down lap back to the beach.

Or, in the shorthand favored by SERC veterans: beach, opening, Creakers, Gashouse, Opening, beach.

The Chas Lap. Click to enlarge.

The Chas Lap. Click to enlarge.

Important Safety Caveats:

  • Avoid swimming outside the Cove alone! You could get injured or killed, and no one would know, possibly for hours.
  • Swimming outside the Cove after 9am is subject to increased boat traffic, windier conditions, and annoying numbers of fishing lines.
  • Not sure if you’re ready for a Chas Lap? Try a few Round-Trip Fort Masons (beach - Opening - first Ft Mason pier - Opening - beach) during a flood current. If you can make it without much trouble, you may be ready to graduate to a Chas Lap.

The Chas Lap is named after South Ender Chas D., who didn’t exactly “invent” this route, but started swimming it so often that people started calling it a “Chas Lap.”



The challenge of a Chas Lap depends almost entirely on the tide (and to a lesser extent, the conditions). It is:

  • Easiest during the slack portion of the tide cycle.
  • Hardest at max flood, due to the long against-current stretch from the Opening to Gashouse.
  • Ill-advised on a rising tide, especially a rising ebb. You don’t want to get caught west of Aquatic Park (“down-river”) when the current begins to exceed your swim speed.

It bears repeating: Beware of attempting Chas Laps on rising tides. The currents can increase faster than you expect, and you can get tired faster than you expect. If you have to be rescued, you will bring shame upon Chas, the South End… really, just about everyone

Varieties of Chas Laps

In order of difficulty:

  • Double: twice back-and-forth along the line betwee:n Gashouse and Creakers. Returning to the beach between the first and second legs is not necessary.
  • Reverse: a Chas Lap on an ebb tide. Breakwater first, then Gashouse. Not recommended.
  • Fully Outside: a standard Chas Lap. Must swim outside Muni Pier on the way out, and outside the breakwater on the final stretch.
  • Inside: Swim outside Muni Pier on the way out. Then, if the current is too strong to finish the final stretch outside the breakwater, swim back along the inside for slacker water.
  • Under/Outside: It is substantially easier to make westward progress from the Opening on a flood tide, if you swim under Muni Pier until it curves around to the north (then cut across the cove to Fort Mason). Watch out for barnacles, though! Then on the final stretch, swim outside the breakwater.
  • Under/Inside: Under the pier on the way out; inside the breakwater on the final stretch. This route will drastically reduce the effect of the currents.
The Creakers (east end of Hyde St breakwater). SS Jeremiah O'Brien in background.

The Creakers (east end of Hyde St breakwater). SS Jeremiah O'Brien in background.

One last thing, and I’ll try to put this gently:

Do not try this unless you know what you are doing.

If you’ve never swum in the Bay before, try going to the Flag and back. If you get tired of running head-first into triathletes along the buoy line, try swimming around the Cove once. Then twice. If you get comfortable in the Cove, try swimming against an ebb down to the Creakers. If you master that, maybe try a RTFM. If you are a fast enough swimmer to get to Fort Mason against a flood on most days, only then should you consider attempting a Chas Lap.

Don’t swim alone. Always check the tide books. Use common sense. Don’t be an idiot.