READ OUT LOUD. Choose which marked text you prefer to practice with - macrons or accent marks - and read the text out loud until you feel comfortable and confident. Then, try reading the unmarked text at the bottom. It should be easy for you after practicing with the marked texts. :-)
MACRONS. Here is the text with macrons:
In fluvium dēscenderat puer, corpus ut ablueret, sed, imperītus natandī, in perīculō erat ut suffōcārētur. Virum ergō, quem forte praetereuntem videt, ut sibi opem ferat, implōrat. Quī illum, dum perīculō līberat, sīc interrogāvit, "Cūr, quaesō, natāre cum nescīrēs, tantīs undārum fluctibus tē commīsistī?" Tum ille, "Nunc mē modo servā (inquit), post deinde increpā."
ACCENT MARKS. Here is the text with ecclesiastical accents, plus some color-coding for the words of three or more syllables (blue: penultimate stress; red: antepenultimate stress):
In flúvium descénderat puer, corpus ut ablúeret, sed, imperítus natándi, in perículo erat ut suffocarétur. Virum ergo, quem forte praetereúntem videt, ut sibi opem ferat, implórat. Qui illum, dum perículo líberat, sic interrogávit, "Cur, quaeso, natáre cum nescíres, tantis undárum flúctibus te commisísti?" Tum ille, "Nunc me modo serva (inquit), post deínde íncrepa."
UNMARKED TEXT. Here is the unmarked text - after practicing with the marked text that you prefer, you should not have any trouble with the unmarked text:
In fluvium descenderat
puer,
corpus ut ablueret,
sed, imperitus natandi,
in periculo erat
ut suffocaretur.
Virum ergo,
quem
forte praetereuntem
videt,
ut sibi opem ferat,
implorat.
Qui
illum,
dum periculo liberat,
sic interrogavit,
"Cur, quaeso,
natare cum nescires,
tantis undarum fluctibus
te commisisti?"
Tum ille,
"Nunc me modo serva (inquit),
post deinde increpa."
IMAGE. Here is an illustration for the story (image source) showing someone in the water - he doesn't look desperate yet:
