AUSTIN (KXAN) — The Lake Travis Independent School District is increasing police presence at Lake Travis High School after an anonymous threat written in black marker was found inside a bathroom.

Lake Travis ISD Superintendent Paul Norton sent a letter to the high school community on Tuesday, explaining the administration was aware of a message found in a bathroom.

Norton says increased security is out of an abundance of caution, and students should still be sent to school, although choices to keep children out are respected and understood. Increased security will be throughout the week.

The district says a full investigation is underway, with Lake Travis ISD police and students encouraged to report any suspicious activity they may see.

Meanwhile, earlier in the day, a picture circulating online gave the false impression there was a threat at Bowie High School in the Austin Independent School District. The district says AISD investigated an emailed photo of guns and determined it was not a credible threat.

Another investigation took place at Rouse High School in the Leander Independent School District. Principal Tonya Thompson said students were held in their rooms for 20 minutes Tuesday as administrators investigated a report of a possible gun on campus. Law enforcement was called, and a student was searched and found to have a BB gun and pocket knife in their possession. An actual gun was not found on campus.

Since last week’s school shooting in Michigan, there have been a number of scares in school districts nationwide.