I'm not sure what cron command you are using, but you need to run the PHP interpreter and pass it the river-fetch.php file.
It looks like (based on the error message, you're just trying to run the river-fetch.php file directly.
Your cron command should look like:
/usr/local/php81/bin/php -q /home/goblesweather/www/www/River/river-fetch.php