The changes in river ice is an interesting topic and interesting in many respects, and I find the authors study thorough and well written. I have some questions and comments to the work below:

An important topic in studies based on ice observations are the uncertainty in the actual data. In my experience and as discussed by the authors there could be differences in how ice is observed subjectively.

• For the data used in the study, have the observers used any guidelines for their registration? E.g. how much border ice must be present before it is recorded? Is total ice cover based on a 100% cover? Is the ice observed in a cross section or over an area? The issue with BI/TIC is mentioned on line 472, is this subjectively evaluated or through any kind of guidelines?
• Did you consider if satellite imagery could be used to verify/check the manual observations just to get some info on the accuracy?

In addition to climatic data, ice formation is strongly dependent on river morphology and hydraulics (as you mention in line 481). How similar is your stations? Can different river condition influence the variability between stations? Can you give a brief overview of the river features?

Do you see a change in discharge over time in this region? Could that have an effect on the freeze-up and break-up timing?

Can you say something on how much the reservoirs influence the flow? Are the storage capacity of the reservoirs large? From the discussion it seems that it might not be only temperature effects that is influencing the ice but also altered flow dynamics. Some more info on this would be good.

Regarding the days with no observations (line 142), I assume the ice condition is considered the same until the next observation? I assume this is what is indicated in line 153-154.

Line 235: What can cause the increase in IC in some stations?

You see an increase in BI in some stations and a reduction in TIC. It is discussed if the increase in BI is a direct consequence of reduction in full ice cover which sounds reasonable. Could you elaborate on this? It seems like the increasing trend in BI may also indicate a reduced amount of ice.

Minor things

“dam reservoir” is a special term, wouldn´t just “reservoir” be enough (or dammed reservoir)?

What is the definition of the hydrological year in Poland?

Line 146-147: “However,….” – I find this sentence difficult to understand, could need some explanation.

Line 177: should it be normal distribution of residuals?

Line 178: Check reference to Student t-test, need an author and not only the year.

Line 183: I assume this means that autocorrelation was no issue?

Line 312: Are the significant anthropogenic impacts only reservoir influence?

Line 363: Are the “four cross-sections” here the same as four gauging stations.

Line 404: Can you say something more on the external factors

My comments, mostly text-editing, are given in the attached pdf.