Where Bela krajina checks if the Kolpa is warm enough

01 / THE PRODUCT

Google had no good answer to “temperatura Kolpe”

In high summer the Kolpa at Metlika reaches 27–29 °C — exceptional for a river — and on a hot Saturday its bathing spots are the main event in Bela krajina. But the question everyone asks before getting in the car, how warm is the water, had no usable answer: the official readings sit in the national agency's hydrological tables, three stations deep, in an interface built for engineers.

So I built the answer — ten years ago, with what I had at the time: a WordPress site on Neoserv shared hosting and a Google Apps Script copying the official readings into a spreadsheet, hour after hour. It ranked, it spread, and it quietly became the place Bela krajina checks the river. The spreadsheet is still filling up today, one row an hour.

For season 2026 I rebuilt it from scratch as a proper product: a real database instead of the spreadsheet, three full language versions, structured SEO, an events calendar and ad space for the providers along the river. The product itself stayed what it always was — one screen with the current temperature at twelve spots, a map with directions, places to stay, events on both banks. No app, no account — a page that loads fast on a phone in a car park.

02 / THE SEASON

Ten weeks carry 83 % of the year

A cold, wet May kept the site under 40 views a day. Then the first heat wave hit on 22 May and views went from 300 to 1,400 in four days. The absolute peak was not the hottest week of the year — it was the first hot weekend after school ended, stacked on the 25 June national holiday: eight of the ten strongest days of the season fall between 19 and 28 June.

August's heat wave was hotter — up to 39.5 °C — and never beat June. First heat is news; August heat is expected, and half the region is on holiday somewhere else.

03 / THE VISITORS

A tool people check, not a site they read

For ten years I thought of it as a small tourism site. A season of person-level analytics says it is an instrument — something closer to a weather app than a destination:

• 90 % of views come from a phone; the daily peak is between 10:00 and 17:00.
• 81 % of visits start in Google — a search for the water temperature or a specific bathing spot.
• 85 % of visits are a single page. People come for one number and leave.
• 89 % of views are from Slovenia, 9 % from Croatia — the river is the border, and the /hr/ version carries the Croatian bank.
• Sunday is the strongest day; a weekend day brings 23 % more views than a weekday.

The clearest signal is loyalty. 70 % of visitors came once. But 882 people opened the site on sixteen or more different days of the season, and the 13 % of visitors who came on four or more days produced 64 % of all views. A small core of locals checks the river the way they check the weather — daily, all summer.

04 / THE WEATHER MODEL

Tomorrow's forecast predicts visits better than today's heat

After the season I pulled the national meteorological archive — daily temperatures and rainfall from the Črnomelj station, sunshine hours from Novo mesto — and correlated them with daily views. Across the whole season, temperature correlates strongly (r = 0.73), but that is just summer being summer. The honest test is the core season, 15 June to 31 August, when every day is warm enough to swim.

Two things fall out of this. Inside the core season, sun beats heat: a cloudy 34 °C day does nothing, a sunny 30 °C day fills the car parks. And tomorrow beats today — the next day's maximum predicts views better than the current one, while yesterday's predicts nothing. People open the site the day before they go. It is a planning tool, and the evening-before check is the moment that matters.

Rain on the day itself costs only ~9 % of views — people already saw it in the forecast. A simple model (temperature + weekend + sunshine + rain) explains 44 % of day-to-day variance; a weekend is worth roughly +239 views, each hour of sunshine +86.

05 / THE WATER

Warm water is the precondition, not the trigger

The surprise in the hydrology data: day to day, water temperature explains almost nothing (r ≈ 0). Water moves on a weekly trend; visits swing daily with sun, weekends and holidays. All July and August the Kolpa was simply “warm enough”, so it stopped being a variable.

Until it wasn't. The storm of 22 August cooled Sodevci from 23 to 16 °C in a single day and the site had its weakest week since June. When the water fell under 15 °C in mid-September, the season switched off within two days. Cold water can end a season; warm water cannot start one.

06 / WHAT DIDN'T WORK

The homepage is too good for its own subpages

Putting every temperature on the homepage was the right call for users — and it cannibalises everything else. The homepage absorbs 75 % of views, so most visitors never open a location page at all:

• Any content living only on a location page reaches a quarter of the audience at best — Vinica, the biggest, sees ~7 % of total views.
• The rafting page converts 36 % of its visitors into a click to a provider, the rental page 52 % — and together they get half a percent of the traffic. Intent without visibility.
• The events listing only came alive in July, two months after the audience did.

And one at my own expense. I have spent years testing other people's interfaces for elements that look pressable but aren't — and my own temperature cards collected nearly 900 rage clicks over the season. People tap the number expecting it to do something.