The animal welfare charity was alerted when the animal was discovered in a car park in Aberfeldy on 17 July.
The male otter, who has been named Ripple, is now being rehabilitated at the Scottish SPCA's National Wildlife Rescue Centre in Fishcross.
Centre manager Colin Seddon said: "We think Ripple's holt may have flooded due to the very heavy rain."
He added: "His mother was likely moving location and has either dropped him or left him behind. Ripple is so young his eyes haven't yet opened but he appears in good condition".
He said otters usually remained in the SSPCA's care until they were at least a year old and mature enough to fend for themselves in the wild.
The Scottish SPCA is caring for a three-week old otter cub found orphaned following severe flooding.