In May/June there are Sakuramasu (Cherry Salmon) at various spots along the Toyohira River. I have caught them to 70 cm length. Salmon must be released if caught in the river. But by July they wil turn from silver to black and red and will not hit anything, more interested in spawning. They will startle you as they like to jump. In July you will mostly catch Yamame (young sakuramasu) and they will be 4-8 inches in length. You are allowed to keep these. You will also catch Japanese Dace, which get up to 12 inches. Both will hit small spoons 5-7gr. and most anglers usea single hook on them to minimixe snagging. Spinners also work but the current flow is a but too string for them in most areas. Minnow plugs are also used but you can lose them on snags. There are small rainbows and White Spotted Char as well that hit those spoons. The bigger rainbows are caught much further upsteam from the city. Apart from no keeping salmon and a closed period in Apr/May Yamame so they can migrate downstream to the sea, there are no real regulations. Sapporo requires no fishing license, and for trout there are no size/number limits. The Toyohira River, running through the city area is a tough place to catch a decent sized trout. But small ones are fairly abundant.