Registration is Open!

Friday, 24 May 2019

In 2017, NOWSA held the first 20k Mercer Island Marathon Swim, or MIMS for short. The event is inspired by the old MIMS in New York: it is meant to be a day where swimmers can meet each other face-to-face and share in a marathon swim that is both challenging yet approachable.

MIMS is held on a Friday in late spring, so it is not a warm swim. In the past, temperatures were in the low 60s. Swimmers should be prepared for cold temperatures, and should be prepared to prove that they have adequate experience and training during the application process.

New format for 2019

We want to grow the event bigger than it was in the first two years, and so we have a new format this year. Each swimmer will be accompanied by a dedicated paddler and a fleet of power boats will be on hand to provide, safety, support, and event observers.

This means swimmers will be responsible for providing a kayak and paddler, and preparing to swim without a boat crew. We’ll be able to provide a rental kayak from a local shop or find you a local kayaker (limited number available), although these are not included in the entry fee.

The event will continue to follow our standard Rules of Marathon Swimming. This is a non-wetsuit event.

See the Info and FAQ page for more event info and instructions.

2019 Swimmer list

The 2019 list of swimmers is here!

What's included in the event?

Your entry fee will cover the following:

  • Swim event fees, including park rental, swag, volunteers, etc

  • Support boats with safety crew and observers

  • Event insurance

  • A NOWSA annual membership. (You may upgrade to a full lifetime membership during the same year by paying the difference.)

  • Tracking on

  • On-shore location at start/finish for gear storage during the swim

What is not included:

  • Transportation, lodging, food.

  • A kayak or paddler.

Fees & How to apply

We still have spots to fill, so registration will continue until either a) we fill up, or b) 1 May 2019. Thinking of signing up? Do it now!

NOWSA reserves the right to reject applications for any reason. Applications received after 11 February 2019 will be accepted on a first-come-fist-serve basis after review, and a 25% non-refundable deposit will be required within 7 days of application acceptance to complete registration.

Use this registration link to apply while applications are being accepted.

Fees for 2019 are


Event Fee

Provided kayak and/or kayaker (if required)


If you really want to swim this year but cant make the event, consider a solo swim.