That's a beautiful pond "helpneeded". Here's the thing... I know you want to save money, but pond filters are not that expensive. You are looking at less than $200 for efficient pond filtration. Looking at that pond, I would assume that it is close to 1000 gallons. I have included a link to a site that sells the type of filter that you need. They aren't expensive but you need two with that pond set up, and I'll explain why. You could get one that is made for more than 500 gallons, but I recommend one of these on each side of your pond, as water movement is a huge issue when it comes to minimizing algae growth. One of these on each side would ensure adequate water movement and proper filtration.
Pondmaster Starter Pond Kit - PMK1250
Also, some one mentioned earlier that concrete is an algae magnet. Very true. Consider the use of pond liner. However, if you provide a proper chemical balance and water movement in that pond, you are going to give algae a hard time when it tries to find a home.
You also mentioned fish. Depending on the fish, you are looking constant water maintenance task when it comes to keeping those fish alive. I don't have much knowledge with out door pond fish, but I do have an indoor aquarium and just maintaining that is a chore. I would imagine that an outdoor pond would be a much larger task. Keep us informed with what's going on. I'm interested to hear how it works out.