We all love catching fish on fly rods and reels. Most of us cut our teeth on trout as kids and have never stopped chasing these beautiful fish.
I remember my grandfather teaching me how to fly fish, I couldn’t have been more than 7/8 years old. The tackle and gear were minimal those days, and we used what we had.
But boy, did we have fun. Along with being taught everything there was to know about chasing trout on the fly. My grandpa also taught me to respect the fish for what it was and its role in nature.
Rainbow trout spawn in the spring. The months can vary based on which hemisphere in the world. The key drivers (there are many) for the spawn is water temperatures reaching optimum temperature and water levels providing rainbow trout migration to spawning gravel.
Every year around spawning time, I would get super excited as I knew that the big fish would be around and we may have a shot at one. This was a short-lived period as no sooner were we ready to fish, the pre-spawn period, my grandpa would call off all fishing for the next few weeks to allow the fish to spawn uninterrupted.
As a kid, I never understood this, and as I grow older, I find myself using my grandpa’s exact words to clients and my kids, ‘LET THEM DO THEIR THING.’
What Time of Year Will Rainbow Trout Spawn?
If fly fishing had a poster child or ‘favorite,’ it would be the Rainbow Trout (Oncorhynchus mykiss). They are the most commonly found trout in many of the USA waters. Originating from the North Pacific, they have made their way down and are now in many of the local waters spread across the US and the world, for that matter.
Pre-spawn rainbows are aggressive, especially the males, and competition to find a suitable mate can be fierce! As anglers, it’s up to us to manage the rivers ethically and ensure our favorite quarry’s sustainability.
Although exact times may vary from area to area, the basic rule is that rainbow trout spawn in the spring. So, with this information, it’s safe to say, January to June in the Northern hemisphere and September to November in the southern hemisphere.
Taking the above into account, there are environmental specifics that play a significant role in influencing the spawn. A few things need to happen for the spawn to occur, and water temperature is the main one, followed by water flow and water quality.
Let’s look at these in more detail.
Factors that Affect Rainbow Trout Spawning
The water temperature is key to the start of the annual rainbow trout spawn. The fish generally wait until the water temperature starts to rise slightly. The water temperature needs to be anything above 42°F / 6°C with the optimal temperature range from 42°f / 6°C to 52°F 12°C for the spawn to start. Once the eggs are fertilized, the trout alevin remains in the ‘REDD’ for a few more weeks until they are ready to vacate the nest.
This would mean January to June in the Northern Hemisphere and September to November in the Sothern Hemisphere. The spawn is shorter in the south due to the quick rise in water temperatures.
Within weeks, these rivers generally climb from the late single digits to the mid to upper teens. The rainbow trout populations have adapted to these changes and tend to spawn a little earlier than the rest, completing a relatively quick cycle. This is a true example of how nature works and adapts to its environments.
It has also been mentioned that the Rainbow Trout are the most resilient to the rapid change of temps of all the trout species. Browns, cutties, and brooks would suffer a lot more and, in most circumstances, not make the spawn and high-water temperatures.
Streamflow is very important for a number of reasons. Firstly, it would be the highly oxygenated water that flows over the nest this is what speeds and aids the spawning process.
The water needs to be at a constant flow, crisp to temperature, and clean.
These are all the factors that contribute to a productive spawn.
Guide Tip: If you live in the U.S. Check out the USGS website for stream flow data. Some of my favorite rivers will even have monitors for water temperature. LINK to USGS
The trout make a nest in preparation for the spawn.
The nest is commonly referred to as the REDD. It is a patch of rocks that has been cleaned somewhat. This is the area in which the fish lay their eggs.
You can quickly notice a REDD pre-spawn or during the spawn by seeing these clean rings of rocks in the shallower parts of the river.
The nest or REDD will naturally be made in an oxygen-rich area of the river to ensure the best chance of survival for the eggs. This is often over finer gravel and cobblestones where the river flows are strong and constant, providing a good supply of oxygen-rich water over the nest.
The high oxygen level is an important key to the healthy, quick development of the trout eggs to alevin to fry and onto parr.
Guide Tip: Oxygen level isn’t talked about much, but the health of a river for trout populations is highly dependent on oxygen. Read this in-depth study done by the U.S. Forrest Service – Rainbow Trout Responses to Water Temperature and Oxygen Levels
How to Fish for Rainbow Trout During the Spawning Season
Before the Spawn
The pre-spawn is often seen as a good time to catch big, more aggressive fish. Those cock fish with the distinct kype and those fat females that are getting ready to lay their eggs.
While there are many trains of thought about fishing during this time of the year, whether you are targeting browns that target the bows or bows that target the browns in their relevant seasons, I always just say; be sure to handle the fish with extreme care and don’t let it fight to go on longer than is needed to bring it in safely.
We need to remember- that this is the time of year that the fish naturally get worked up and are full of energy to spawn, so to fight them on a rod and reel would just diminish their vital energy levels needed to spawn successfully. That said, try to time your fishing trip with enough time for the fish to recover in time for the spawning motions.
Taking from this what you want, pre-spawn trout can be great fun provided you act and fish ethically, ensuring the safety of the fish.
Setup- There’s nothing different here, just your usual setup, but I suggest upping your tippet size! If you usually fish a 5X on your stretch of water, fish a 3X instead, as the fish hit harder and are generally more aggressive. This heavier tippet will also help to bring the fish in faster, reserving most of its energy.
Flies- When it comes to fly selection, fish anything with a hot spot or trigger in the pattern. Egg Patterns, Egg Sucking Leech and Black Stone Flies are great choices. Luminous colors are massive attractors and will most often get the job done. For the rivers, a small jig bugger with a hot spot tail or collar will work well.
In the still waters, the angler’s fish blobs and egg patterns pre-spawn to capitalize on the trout’s natural habits at this time.
Whichever flies you choose to fish, fish them barbless and slightly larger than the usual size, and you will be on for a great time.
During the Spawn
This period is one of the hottest conversed topics in the fly-fishing world. To fish during the spawn or not.
An angler’s ethics can come into question if found to be fishing during the annual rainbow spawn. Again, this is a very subjective topic, and these are my opinions to note.
I believe that the spawn should be a NO FISHING time. Spend the time to fill the gaps in the fly boxes.
Let the fish do their thing, ensuring that rivers are stocked in the future.
Here’s the tricky part- once the redds have been made, eggs laid, and fertilized, nature does its thing. But what happens to those eggs post-spawn?
A laid trout egg hatching is called an alevin. These alevins remain protected in the redds for a few weeks post the spawn. The problem comes in at this time as the redds silt over quickly once the hen has left, and they become almost impossible to notice. So early-season angler can walk straight through the redd without the slightest knowledge of it even being there and the damage he is doing!
The whole no fishing during the spawn, wasted!
Should You Target Spawning Rainbow Trout?
As I have mentioned in the above sections, targeting rainbows during their spawn is not recommended. I’m of the opinion that it’s best to leave them to do their thing. There are plenty of other species to target during this time.
Brown trout are my target during the rainbow spawn. The browns are great to target during this time, and they frenzy feed on the washed-out eggs that move downstream. The browns eat hard and quite willingly.
At this time, I fish egg patterns, and again luminous colors work well and trigger the browns. It is best to sight fish these fish as you will see them hanging off the seams eating at will.
I use a dropper rig for this time of year with two egg-type patterns. I like to use an unweighted egg pattern as I want the fly to drift as naturally as possible.
What is a Redd, and What’s it Look Like?
A redd is basically a trout nest. It’s an oval, circular shape of cleaned rocky bottom and pebbles that the trout hens clean in preparation for laying their eggs. The redds are generally always in a tributary with high, oxygenated waters flowing over them.
It always helps to walk the river on the bank during the spawn to identify the redds during the spawn. It is then easier to avoid these areas post the spawn, so one doesn’t walk through the redds. The redds become very washed over and near impossible to see.
This is still an interesting area of conversation; many nature boards and groups are now marking this area for this exact reason. This helps these areas to remain untouched and for the trout alevin to complete their cycle.
Pro Tip– as a guide, it’s best to GPS mark the redds on your local river so when the season opens again, you can comfortably avoid these areas with your clients.
Will Rainbow Trout Die After Spawning?
There is often a misconception about which fish die naturally post their spawn. In short, salmon is one of the only species that return to the same ground they hatch on and die post their spawn. Their energy levels are so depleted that they are often easy pickings.
Rainbow trout, along with all other trout species, don’t die naturally post their spawn. Sure, there are several challenges that could result in their death post-spawn, but it is not natural for the trout to die once the eggs have been laid and fertilized.
Frequently Ask Questions About Rainbow Trout Spawning
When in Montana?
Montana has some great fishing. It’s best to try and miss the crowds over the peak times. The Rainbow trout spawn from April to July when the water is around 50°F / 10°C. So, try to plan your trip accordingly. Should you be fishing past the spawn, be sure to check with your local office regarding any markings of redds that you can learn about. https://guiderecommended.com/where-to-go/montana-fly-fishing/
When in Colorado?
February to May is your ideal spawning time out in Colorado. Water temps are a little lower, around ~44°F (6-7°C), but the fish love this time. Check out the link for more in for on this area. https://guiderecommended.com/fly-fish-colorado/
When in Wyoming?
Wyoming’s spawn period is from April through to May. The beauty of this area is that you can ignore the rainbows completely and focus on the browns, specifically during this time. Places like Flat Creek come to mind targeting The Fine Spot Cutthroat Trout.
Please read the below like for more info. https://guiderecommended.com/fly-fish-wyoming/
Are you looking for some great How To Fly Fish Articles? Checkout this list:
- How to Fly Fish for Bass with Poppers with 👈 Easy to catch and fun to fight, fly fishing for bass is amazing!
- How to Fly Fish for Bluegills 👈 These amazing fish are all over the USA. I like to call them the “Gateway Drug to Fly Fishing”
- How to Fly Fish for Brook Trout 👈 Find the cleanest, coldest, most beautiful streams and I’ll bet Brookes are present.
- How to Nymph Fish 👈 Step by Step details for setting up, presenting and catching trout with nymphs.
- How to Fly Fish for Salmon 👈 Image hooking into a +25 pound King Salmon in a river and your Fly Rod breaks! Seriously this happened to me on my first trip.
One More Cast to Rainbow Trout
It all boils down to ethics, in my opinion. As you now know, there is a whole lifecycle for us to preserve, and it’s up to us as the anglers to do so.
If we want to teach our grandkids the ways which were taught to us, then we must take action now! I’m not saying we can’t fish; you can catch anything on a fly rod, so we have plenty of other species to go after during the rainbow spawn.
Let’s give these fish the necessary time to do what they need to and help ensure many more years of great fishing fun. Tight Lines!
Fly fishing has been my passion and pursuit for the past 20 years. I am a South African based fly fisherman who loves nothing more than spending a day on the water. Fly fishing is more than catching fish, being in the outdoors with good friends and family is what it is all about.