From late June to early August, depending on water levels, you can float down the Boulder Creek in tubes. During the early spring when the water is high, the creek is very dangerous and only suitable for experts with kayaks. When the water gets turned down a bit, it is fairly safe, but can still be an exciting ride in places.
The gas station on Arapahoe and Broadway has an air hose that they let the public use for free so you can transport your tubes flat and fill them when you get to the creek. The station also sells tubes. Parking can be a challenge (as usual in downtown Boulder).
Most people tube in the area that goes through Eben G Fine Park. This area has a series of small ponds and small waterfalls that can be fun to ride through on tubes. Eben G Fine Park also has a good-sized park with shade and picnic areas that can be nice to hang out in on summer days.
The best place for kids to tube is by the library between the 2 pedestrian bridges. This area is fairly shallow and moves slow most of the time, so it can be a good spot for small kids. The area by the library is also good for kids because it has picnic areas and bathrooms close by at the library.
The creek is tube-able from Eben G Fine Park to the library when the water is at a good level, but it is not always the best ride. Many times the water can be too shallow in spots and you can get stuck on the rocks risking a flat tube. Some years there can be tree branches that stick out in the creek and can be annoying to try to tube around. It’s usually not the best ride, but a few people do it when the water is high enough.
By August, the creek starts to get lower and most parts of it are too shallow to tube. When it gets shallow, sometimes you can still get a few runs in at the kayak ponds or the kids can still float around the library area.
When tubing the Boulder Creek, it is important to wear shoes or water socks because the rocks can be hard on your cold feet when getting out of or walking around in the creek. Flip flops are easily lost and will disappear down the creek within a few minutes. If the water is high and you see no one out on the creek, it is probably too high. You might have to wait a few days until the water calms down.