Oyston believes that it was a decision that he had to take.
"This decision is to give us the best possible chance of surviving in the Championship, the change was necessary," he told the Blackpool Gazette.
"We have to turn things around and give someone the chance to bring some fresh players in and brighten things up. We have left it as long as we possibly could, things just weren't improving.
"It was something we had to do."
Lee Clark, who recently lost his job at Birmingham City, is reportedly in the frame to replace Riga.