The Egyptian Public Prosecution issued orders to imprison Abdel Nasser Salama, the former editor-in-chief of Al-Ahram newspaper, for 15 days pending an investigation into claims he financed terrorism.
Salama was charged with financing terrorism and joining a terrorist group established in violation of the provisions of the law; in reference to the Muslim Brotherhood.
His arrest came after he called on President Abdel Fattah Al-Sisi to step down and be put on trial because of what he called "the heavy defeat against Ethiopia, and wasting Egypt's historical right to the waters of the Nile".
In a post he posted on Facebook last week, Salama asked: "Why does President Al-Sisi not have the moral courage, and declare his direct responsibility for the heavy defeat against Ethiopia, and for wasting Egypt's historical right to the waters of the Nile?"
Authorities arrested Salama at his home yesterday evening, in implementation of the Public Prosecution's decision, after accusing him of spreading false news on social media and questioning state agencies and institutions.
Salama had been appointed editor-in-chief of Al-Ahram newspaper when the Muslim Brotherhood was in government and until January 2014.
Ethiopia is building a $5 billion dam near the border with Sudan it says will provide the country with much-needed electricity and economic regeneration. Egypt believes it will restrict its access to Nile waters.
Egypt is almost entirely dependent on Nile water, receiving around 55.5 million cubic metres a year from the river, and believes that filling the dam will affect the water it needs for drinking, agriculture and electricity.
Cairo wants Ethiopia to guarantee Egypt will receive 40 billion cubic metres or more of water from the Nile. Ethiopian Irrigation Minister Seleshi Bekele said Egypt has abandoned this demand, but Egypt insists it hasn't and issued a statement to this effect.
Al-Sisi signed an agreement with Sudan and Ethiopia in 2015 which he said will "achieve benefits and development for Ethiopia without harming Egypt and Sudan's interests". However, many have critised the deal as having given away Egypt's rights to the Nile.