Trend and Seasonality

I have daily water quality time series data for about 5 years (1850
observations). I want this series to be deseasonalized and detrended
for further analysis. From the scatter plot I can observe the trend. I
plotted the autocorrelation and partial autocorrelations for the daily
data but could not figure out whether there is seasonality or not, it
is not very clean. I have access to SAS and NCSS, although not
confident on SAS. How can I find whether there is seasonality in the
series? and if there is seasonality, how can I remove those?

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