Is your algae the free floating type or the attached (blanket weed) type? If it's frre floating, a UV sterilizer can help, but these tend to be expensive and you need to replace the lamps frequently (at least yearly). Fish and snails won't be a lot of help with this type.
If you've got an attached algae, fish or snails will be more useful, but they may not survive over your winter. A UV unit will reduce the reproduction, but it can't do anything for the algae that's already growing.
There are a few things you can try. The first is to control the nutrients in your pond. Don't allow any leaves or other debris to stay in the pond - get them out when you first notice them - these will eventually decompose and add to the nitrates and phosphates in the pond, which become alge fertilizer. If you have pond plants, don't use any fertilizer until they're actively growing and then, only use the pellets that you put right at the plant roots to target the plants you want in the pond. If you've got fish, be sure you aren't over feeding them. All this builds up in the pond to feed the algae. Pond plants will also absorb some of these nutrients, but until they start growing in your climate, you can reduce the amount by doing a partial water change (around 25%) with a siphon, just like your pond was an aquarium - at least if your pond is a practical size to do this. You may need to repeat this on a regular basis. This will also reduce the amount of algae, if you have the free-floating type.
Algae also needs light to grow. Once it gets warm enough, using floating plants (water hyacinths or water lettuce) or plants with floating leaves (water lily) will shade the algae to keep it from being able to use photosynthesis to make food.
If you've got attached algae, you should try to scrape as much as you can by hand and remove it from the pond altogether. If you leave it after you scrape it off, it will decay and add to the nutrients and use up oxygen as it decays, and this can have an effect on any fish you might have in the pond.
Once you've gotten as much out as you can, visit a local pond/garden center and see if you can find barley straw. This can help prevent new algae. See info on this, plus some other ideas on pond algae control from the links I'll post below.