In R, subset data using longest contiguous stretch of non-NA values - r

Question

I am prepping data for linear regression and want to address missing values (NA) by using the longest contiguous stretch of non-NA values in a given year and site.
I have tried na.contiguous() but my code is not applying the function by year or site
Thanks for your assistance
The test data is a multivariate time series that spans 2 years and 2 sites. My hope is that the solution will accommodate data with many more years and 32 sites- so some level of automation and qa/qc is appreciated.
library(dataRetrieval)
library(dplyr)
# read in Data, q is discharge and wt is stream temperature
wt<-readNWISdv(siteNumbers=c("08181800","07308500"),
parameterCd=c("00010","00060"), statCd=c("00003"),
startDate="1998-07-01", endDate="1999-09-30" )
dfwt<-wt%>%
group_by(site_no)%>%
select(Date,site_no,X_00010_00003,X_00060_00003)%>%
rename(wt=X_00010_00003,q=X_00060_00003)
#Subset summer season, add dummy air temp (at).
dfwt$Date<-ymd(dfwt$Date, tz=Sys.timezone())
dfwt$month<-month(dfwt$Date)
dfwt$year<-year(dfwt$Date)
df<- dfwt %>%
group_by(site_no)%>%
subset(month>=7 & month<=9)%>%
mutate(at=wt*1.3)
# add NA
df[35:38,3]<-NA
df[155,3]<-NA
df[194,3]<-NA
test<-df%>%
group_by(site_no, year)%>%
na.contiguous(df)

Answer 1

Using a for loop I found the following solution,
library(zoo)
library(plyr)
library(lubridate)
zoo(df)
sites<-as.vector(unique(df$site_no))
bfi_allsites<-data.frame()
for(i in 1:2){
site1<-subset(dfz, site_no==sites[i])
str(site1)
ss1<-split(site1,site1$year)
site1result<-lapply(ss1,na.contiguous)#works
site_df <- ldply(site1result,data.frame)
bfi_allsites<-rbind(bfi_allsites, site_df)
}
head(bfi_allsites)