Fortran (GFortran), 145 138 134 128 bytes

character*8s;do i=1,100;s=''
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s=trim(s)//'buzz'
if(s=='')write(s,'(i0)')i
print*,s
enddo
end

Try it Online!   _{134b 138b 145b}

On line 4 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.

Fortran (GFortran), _{145 138 134 128} 125 bytes

character*8s;do5 i=1,100;s=''
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s=trim(s)//'buzz'
if(s=='')write(s,'(i0)')i
5 print*,s
end

Try it Online!

On line 4 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.
_{128b 134b 138b 145b}

Fortran (GFortran), 145 138 134 129 bytes

character*8 s;do i=1,100;s=''
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s=trim(s)//'buzz'
if(s=='')write(s,'(i0)')i
print*,s
enddo
end

Try it Online!   _{134b 138b 145b}

On line 4 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.

Fortran (GFortran), 145 138 134 128 bytes

character*8s;do i=1,100;s=''
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s=trim(s)//'buzz'
if(s=='')write(s,'(i0)')i
print*,s
enddo
end

Try it Online!   _{134b 138b 145b}

On line 4 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.

Fortran (GFortran), 145 138 134 bytes

character*8 s;do i=1,100
write(s,'(i0)')i
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s='buzz'
if(mod(i,15)<1)s='fizzbuzz'
print*,s
enddo
end

Try it Online!   _{138 bytes    145 bytes}

On line 2 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.

When the Gnu compiler implements ternaries (expressional IF) we might be able to save more bytes.

Fortran (GFortran), 145 138 134 129 bytes

character*8 s;do i=1,100;s=''
if(mod(i,3)<1)s='fizz'
if(mod(i,5)<1)s=trim(s)//'buzz'
if(s=='')write(s,'(i0)')i
print*,s
enddo
end

Try it Online!   _{134b 138b  145b}

On line 4 we write the current value of i into the string s. This greatly simplifies the subsequent print statement.