As a sweltering heat wave brought temperatures north of 90 degrees and high humidity to Massachusetts for the third straight day on Thursday, nearly 20 beaches across the state were closed, according to the state’s public water quality dashboard.

In all, 18 beaches across Massachusetts were closed as of the 9:30 a.m. update to the dashboard. The closures spanned from Great Barrington in Western Massachusetts to Boston in Eastern Massachusetts to beaches on Cape Cod and the Islands. Of the 18 beaches closed in the state as of Thursday morning, two-thirds — 12 of the 18 — were shuttered due to an excess of bacteria in the water.

The remaining closures were attributed to harmful cyanobacteria blooms and “other.”

• Read more: Here’s how hot it will get on Thursday in Massachusetts amid the heat wave

In Great Barrington, Lake Mansfield was closed, though the dashboard listed only “other” as a reason. In the eastern part of the state, in Boston’s Dorchester neighborhood, Tenean Beach was shuttered due to an excessive amount of bacteria in the water.

On the Cape, Attaquin Park in Mashpee was closed due to a harmful cyanobacteria bloom, the same reason given for the closure of Miacomet Pond in Nantucket.

Two beaches in Salem were closed on Thursday — the most in any municipality — with Camp Naumkeag closed due to “other” reasons and the back of Children’s Island closed because of bacteria.

• Read more: These beaches have the best — and worst — water quality in greater Boston, report finds

“If a beach is closed, do not swim or enter the water at that location to avoid risk of illness,” the dashboard warns.

The dashboard is updated twice a day, once in the morning and once in the afternoon, and shows the results of recent water quality tests at beaches across the state. More than 1,100 public and semi-public beaches in the state are regularly monitored.

And despite the closures, state officials say the beaches are still perfectly safe for recreational activities aside from swimming.

The full list of closures is below. If you can’t see the chart, click here.

If you are a Native American living in Massachusetts, you may qualify for tuition assistance at a state college or university, including UMass Dartmouth and Bristol Community College.

The Massachusetts Executive Office of Housing and Livable Communities (EOHLC) Commission on Indian Affairs (CIA) says, “Over the last three decades, the Massachusetts Commission on Indian Affairs has assisted in the determination of eligibility of Native Americans living in Massachusetts for tuition credits (formerly known as the tuition waiver) at state colleges and universities.”

The CIA is authorized by the Massachusetts Department of Higher Education to “certify that applicants are of Native American descent” and eligible for the tuition break.

The Commission on Indian Affairs “uses membership in a Massachusetts tribal group (tribe, band, or clan) that is acknowledged by the Commission as a legitimate, historical tribal group as a criterion for making decisions on the eligibility of students for the tuition credit.”

Some Native Americans whose tribes are outside of Massachusetts may also be eligible for tuition credits.

To be considered for the tuition credit, applicants must be Native American, a Massachusetts resident, and enrolled in an undergraduate degree program at a Massachusetts college or university.

The CIA’s webpage has a link to a list of participating colleges and universities and a link to the Tuition Credit Form. Proof of residency and tribal membership/affiliation is required.

The deadline to apply for the tax credit for the fall semester is July 15, and December 15 for the spring semester.

The site can also help with housing needs.

A firewall designed to prevent cyberattacks and hacking was to blame for the 911 outage that hit Massachusetts this week, state officials said Wednesday. Massachusetts’ 911 system was down for about two hours Tuesday, making it impossible for anyone to reach emergency services using the number. In a statement Wednesday, the Massachusetts State 911 Department said it determined the outage, which lasted from 1:15pm to 3:15pm, was due to a safety feature that prevents cyberattacks, though the reason for that is still under review, the AP reports.

While some calls didn’t go through, the state said the system “allows dispatch centers to identify the phone number of callers and return those calls.” As a result, the department was not aware of any emergencies being negatively affected by the outage. At the time of the outage, Boston Police Commissioner Michael Cox said it was important for residents to know alternative ways of getting help, particularly given the hot weather heading toward the Northeast. He advised the public to contact local police departments if necessary.

In another recent 911 outage, services in four states were interrupted when a crew installing a light pole cut into a fiber line. “You and I and everybody take 911 for granted,” Brian Fontes, chief executive of the National Emergency Number Association advocacy group, told the New York Times on Tuesday. “We just always expect it to work. And, to be truthful, it works very well on good days.” He added: “Not every day is a good day, as we’ve seen in Massachusetts today.” (More 911 stories.)