I caught this fish in Chequamegon Bay. I was wondering how much this fish weighs. This fish is 23.5 inches long. I was also wondering if this is a steelhead or a rainbow?

looks like a rainbow and my guess would be about 3 1/2-4lbs

Don't know about where you live but up here, a Steelhead is classified as being 50cm or larger (just under 20 inches). To make a VERY general claim, I've found Steelhead to be more of a slim "bullet" shape while true resident bows are more football-shaped. However this is not a great way to ID between the two; just what I've seen from my experience. If the bows in your area get that big normally, it very well could be a bow. 

 

For what it's worth (and I definitely could be wrong), it looks like a Steelhead starting to show its spawning colours.

From what I've read the rainbow and steelhead are basically the same fish, but are differentiated by where they live and how big they get.  If they live in the Great Lakes they are called steelhead, so you caught a steelhead.  I think...

Some people call them all steelhead, but a rainbow trout is a trout that spends its whole life in fresh water and a steelhead will spend time in the ocean and make its way to freshwater to spawn so steelheads are just a name for rainbows who lived in saltwater but since lake superior is connected to the atlantic ocean it may be a steelhead so my guess is as good as anyone elses lol

Thanks guys!

All steelhead are rainbows. Some rainbows become steelhead. That fish looks around 5 lbs. To me, I'd call it a big rainbow.

Could be either. Nice fish though!

That would be a steelhead. Here is the definition from Wikipedia.

 

The rainbow trout (Oncorhynchus mykiss) is a trout and species of salmonid native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coastal rainbow trout (O. m. irideus) or Columbia River redband trout (O. m. gairdneri) that usually returns to fresh water to spawn after living two to three years in the ocean. Freshwater forms that have been introduced into the Great Lakes and migrate into tributaries to spawn are also called steelhead.

Dwight, all "rainbows" and "steelhead" we're merged into O. mykiss in 1988. Genetic testing revealed their DNA to be identical. The difference is a physiological change called smoltification, meaning they leave the streams to persue a pelagic lifestyle, only to return to spawn. The OP's fish sea a bit small to be a steelhead, but it's really hard to tell with the kype jaw. My dad always told me that in order for a rainbow to be a steelhead, it had to be over 30", lol.

The difference is a physiological change called smoltification, meaning they leave the streams to persue a pelagic lifestyle, only to return to spawn. 

 

This is what I always understood as the difference. The Pelagic lifestyle is the key. Since the great lakes are such large bodies of water they are included as seas or oceans, they just don't have saltwater except for the St Lawrence. The other key is that the steelhead make a migration to return to their streams of origin to spawn. In PA waters they release the hatchery smolts in all the creeks that have access to Lake erie so on the return they are more evenly distributed.

They do the same here. Makes for a heck of a post spawn pike fishery, lol.