Hi Keith your router appears to be the Belkin F5D7632uk4A 54Mbps ADSL Wireless Router (5 not S in the F5D part)
I assume that you know how to access the router through its IP address in the web browser and how to log in.
Once you are logged in you will see a Firewall section on the left side menu.
In that section it should have an option to enable or disable the firewall.
Assuming that you have the user manual in PDF form its shown on sect 1:43 on the one I downloaded but it doesnt explain exactly how to get into that setting so you may have to click on a few links from the firewall section.
To confirm that it is the routers firewall that is blocking your site disable the firewall, dont forget to click Apply Changes, it may ask you to reboot the router, some routers do some dont.
When the firewall is disabled try and connect again to the fishing site.
If you can then re eanble the firewall again.
Your router has an URL blocking feature but I cant see why it should have got thats sites address, listed, if it actually has.
Have a look in the Firewall> Client IP filtering section, page Sect1:46 in the manual and check that the WWW with URL Blocking box isnt ticked.
Unless you have blocked some intentionally if it is ticked then untick it and click Ok and then Apply Changes.
If you have intentionally blocked some URLs then leave it ticked and edit that part to remove the fishing sites url from it.
I hope this helps, unfortunately the manual is quite good if the router was on my pc but not as good as it should be for me to be able to explain each step fully to you
Let me know how you get on with it