In 1897, if you mean Claude Monet. "When did HE paint ...? is an impossible question.
How can I know who you mean????
Water Lilies
Is it not obvious? He had this big pond made and saw to it that the water-lilies grew there in abundance just so he could paint this, his favorite subject.
monet
Claude Monet
He made hundreds of water lilies paintings, in all colors and shades.
He made hundreds of water lilies paintings between the 1890s and 1926.
Again and again during the last 30 years of his life.
Because they were his favorite subject between the 1890s and 1926.
Because he loved his water lily pond, which always looked different from the day before.
Oil paint on canvas.
He was an impressionist so it is very likely that he painted using the plenair technique.
Can't find an exact figure. Anyway more than 60.