The company that runs Lake Titicaca as a business: hydrofoils across to the Isla del Sol, the Andean roots and the Inca steps, and their own infrastructure at Huatajata on the Bolivian shore. If you want the lake done properly rather than by a launch from the Copacabana quay, this is the operator the rest of the trade books through.
The office is on Camacho in the old centre of La Paz. They publish a landline and an emergency mobile and no WhatsApp; booking goes through the form or the email.