Agnes Heller, a prominent Hungarian philosopher and dissident who repeatedly found herself unwelcome in her own country, died on July 19 while vacationing on Lake Balaton in western Hungary. She was 90.

Her son, Gyorgy Feher, said Ms. Heller had gone for a swim, a favorite activity, when her body was found floating in the lake. She had been staying at the summer resort of the Hungarian Academy of Sciences in the town of Balatonalmadi.

The cause of death was not immediately clear. The police, Mr. Feher said, saw no sign of a heart attack or aneurysm. “So what can one say?” he said by email. The police ruled out the possibility of a crime, according to the Hungarian news site Hungary Today.

Ms. Heller, a prolific, wide-ranging writer in multiple languages, explored Marxism, ethics and modernity as well as everyday life. Her eventful life included losing her father in the Holocaust, falling into official disfavor after the Hungarian uprising of 1956, and, most recently, speaking out against Viktor Orban, Hungary's right-wing prime minister.