Following information in more detail can be found here:
https://mrsc.org/explore-topics/legal/open-government/open-public-meetings-act/open-public-meetings-act-basics

Overview

The Washington Open Public Meetings Act (OPMA), codified in chapter 42.30 RCW, requires that all meetings of governing bodies of public agencies, including cities, counties, and special purpose districts, be open to the public.

The OPMA contains specific provisions regarding regular and special meetings, executive sessions, the types of notice that must be given for meetings, the conduct of meetings, and the penalties and remedies for violations.

What Is a "Meeting"?

A "meeting" under the OPMA occurs when a quorum of a city council, board of county commissioners, or other governing body (including certain kinds of committees) gathers with the collective intent of transacting the governing body's business. In order to be valid, ordinances, resolutions, rules, regulations, orders, and directives must be adopted at meetings conducted in compliance with the OPMA.

Meetings do not have to be in person to be subject to the OPMA. Meetings can occur by telephone, email, or other electronic media.

Who Is Required to Comply?

The following local government bodies are required to comply with the OPMA:

• Governing bodies of public agencies: city and town councils, boards of county commissioners or county councils, or special purpose district boards of commissioners.
• Governing bodies of subagencies, including planning commissions, library boards, parks boards, and civil service commissions.
• Certain committees of governing bodies that act on behalf of (exercise actual or de facto decision-making authority for) the governing body, conduct hearings, or take testimony or public comment.

Penalties for Noncompliance

Any action taken at a meeting held in violation of the OPMA is null and void. See RCW 42.30.060(1).

Any member of a governing body who attends a meeting knowing that it violates the OPMA is subject to a potential personal liability of $500 for the first violation and $1,000 for a subsequent one. See RCW 42.30.120(1)(2).

Any person who prevails against an agency in any action in the courts for a violation of the OPMA will be awarded all costs, including attorney fees, incurred in connection with such legal action. See RCW 42.30.120(2).

Training Requirements

All members of governing bodies must complete OPMA training within 90 days of taking the oath of office or assuming duties (RCW 42.30.205). A refresher OPMA training is also required every four years. For more information, see the Washington State Attorney General's webpage on Open Government Training.

MRSC and the Association of Washington Cities (AWC) have created an OPMA online course to help mayors and councilmembers fulfill these training requirements.