It may have pulled more than 3 rivers, but something in one of the JSON files is causing the page to stop after displaying 3 rivers.
Please post your ./River/river-config.php here and I'll try to replicate the issue for debugging. Also post the text file from the cron job that runs river-fetch.php.
These aren't original scripts by me, so I'd unfortunately not included extra debugging stuff in them like I usually do.

It would also help to add the following after the starting <?php on wxriverpage.php:
error_reporting(E_ALL);
ini_set('display_errors','1');
so we can see where the Fatal error is happening.