Degrees of Difference

Nick Simonson

By Nick Simonson

On a morning drive to school, my oldest son and I filled the commute with a discussion about the nature of cold-blooded animals, such as snakes and lizards and fish, versus warm-blooded animals like mammals and, of course in that category, people like him and his little brother.  From the falling iguanas which took headlines during a cold snap in south Florida this winter, to the fish preparing to make their spawning moves – or even just get a little more active for anglers to pursue – the temperature in the world around those cold-blooded creatures dictates what they do.  At no other time of year does water temperature factor more into the moves of fish than in the spring. 


As waters warm, fish become more active, putting on the feed bag to prepare for the spawn and even making those first forays into the shallows to set up for the annual act. Species by species, as the temperature in the aquatic world around them rises, so do their activity levels, making them easier to target and catch.  The trick is knowing the temperatures that get them going, and where those temperatures are likely to be found on a flow.


Fish Facts


Whatever the target may be, each species moves in spring at varied water temperatures.  Most notably, pike are active in the coolest conditions, spawning earlier than many gamefish species.  They can spawn in waters as cold as 40 to 45 degrees Fahrenheit, which can happen quickly if the sun warms runoff, or a strong inflow of dirty melt water darkens flows and makes them warmer, even if there’s ice on a main lake. Walleyes will spawn when waters are in the upper forties, and smallmouth bass stage when water temps get into the upper fifties and will spawn when the water gets over 60 degrees or so. Knowing when fish spawn will also help set up the timetable of when they start their seasonal moves. 


Keeping an eye on the daily data measured at USGS locations which is reported on the internet or utilizing a simple dip thermometer when fishing the cool flows of spring will help track changes in water temperature and provide insight as to whether fish may be on the move.  Note as well that resurgent cool conditions may stall certain fish movements or prolong staging activities resulting in a compressed spawning period or a change in the nature of fish after a cold front passes in spring, when waters are more susceptible to cooling under the influences of weather.


Where to Go


Shallower portions of rivers, feeder creeks, and the deltas that connect the two are often attractive to springtime fish and depending on substrate and structure can draw a number of species in at the same time or swap them out from one week to the next.  A solid run of pike could be replaced with walleyes in the same space a few days later, and those smallmouth bass will fill the gap in the following weeks as well.  Flows near the headwaters that are fueled by the discharge from a dam will generally be as cold as the depths of the reservoir above and stay that way for longer, while those areas downstream, with the influence of warmer runoff may see fish movements sooner. 


Utilizing maps of a flow, and previous experience along with the impact of melt water, runoff from spring rains and even springs and seeps to figure out those likely spots where rivers will warm faster, starting fish on their spring movements sooner. Consider too microcosms of the greater flow.  Culverts which drain city streets and small gullies that move spring water can attract fish to pockets that are warmer than the rest of a river.


Often overlooked in the grand scheme of things, increases in temperature, even by just a degree or two on a sunny spring day, can send fish moving quickly upstream and cause an uptick in activity.  Monitor those changes online and in person and make notes this time of year to compare with future seasons and put the full fishing picture together, while increasing the odds of success in the time on the water at hand.

Featured Photo: Making Moves. Walleyes will make their seasonal spring moves when water temperatures get into the 42-to-47 degree range and will typically spawn when temperatures are in the 48-to-54 degree range. Anglers keeping tabs on their activity level are wise to factor these data points into their plans. Simonson Photo.

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