I am making a plot using ggplot and cannot get the legend to show up. I’ve tried looking through other solutions but still can’t figure it out. It used to work for me, but I think that I may have used some code in the past that messed it up if that makes sense?

Plot0<-ggplot() + 
  geom_line(data=Sandusky8, aes(x=ProperDateTime, y=TKN), color='grey54')+
  geom_line(data=SanduskyA, aes(x=ProperDateTime, y=TKN), color='blue')+ 
  geom_line(data=SanduskyB, aes(x=ProperDateTime, y=TKN), color='red')+
  scale_x_datetime(date_labels = "%Y")+
  labs(title="Total Kjeldahl Nitrogen in the Sandusky River from 1974-2023")+
  xlab("Year") + ylab("TKN (mg/L)")

Plot0 + theme(legend.position = "right")

resulting graph