Lamar Valley in Yellowstone

Sure there are mosquitos but they are not overbearing. Just wear repellant and you will be fine.

Another very short but worthwhile hike in Lamar Valley is the Trout Lake trail. At Trout Lake, you can see the cutthroat trout returning to spawn, which is cool if you're into natural history. There are usually some interesting waterfowl species around, too.

A good view point for the Lamar is the Hike up Specimen ridge. It is dry and moquitos shouldn't be much of an issue. The rivers are dropping after the second week of June and by the end of July it will be easy to find a place to cross. Slough creek is a pleasant walk. I once hiked up the little pass from the road to just above Pebble Creek and climbed up Sunset, Meridian and Wolverine peaks, all of which afforded excellent views and present no technical challenges. Are you talking about day hiking or do you want some over night suggestions as well?

A day hiking, it's a pitty but we don't have more time because we would like to go to Glacier NP.

At the end of july we'll be difficult to cross rivers in Lamar Valley Trail?. I don't like very much barefoot in rivers

Yes, there will likely be stream problems on the Lamar trail then. Runoff peak can last through June depending on snowfall up high. Still its worth it. Just hold socks and shoes up and wade. It'll wake you up for sure!

Ed